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All Textbook Solutions for Conceptual Physics: The High School Physics Program
Fill in the blanks: Newtons first law is often called the law of ____; Newtons second law highlights the concepts of force, mass, and _____; law is the law of and; Newtons third ______ and ________.Three sets of double boxes rest on a table. Rank the following from greatest to least. a. the normal force that the table exerts on the sets. b. the normal force exerted by the bottom block on the top blockA van exerts a force on trailers of different masses m. All velocities v are constant. Compared with the force exerted on the trailer, rank the magnitude of force the trailer exerts on the van. Or are all pairs of forces equal in magnitude?Each of these boxes is pulled by the same force F to the left. All boxes have the same mass and slide on a friction-free surface. Rank the following from greatest to least. a. the acceleration of the boxes b. the tension in the rope connected to the boxes on the right in B and in C24AYour weight is the result of the gravitational force of Earth on your body. What is the corresponding reaction force?Why can you exert greater force on the pedals of a bicycle if you pull up on the handlebars?Consider the two forces acting on a person who stands still, namely, the downward pull of gravity and the upward support of the floor. Are these forces equal and opposite? Do they comprise an action—reaction pair? Why or why not?If you walk on a log that is floating in the water, the log moves backward. Why?Why is it easier to walk on a carpeted floor than on a smooth, polished floor?If you step off a ledge, you accelerate noticeably toward Earth. Does Earth accelerate toward you as well? Explain.When a racquet hits a tennis ball, action and reaction forces occur between the racquet and ball. What other action—reaction pair of forces occur for the ball both before and after interaction with the racquet? Neglect air resistance.Suppose you're weighing yourself while standing next to the bathroom sink. Using the idea of action and reaction, explain why the scale reading will be less when you push down on the top of the sink. Why will the scale reading be more if you pull up on the bottom of the sink?When a high jumper leaves the ground, what is the source of the upward force that accelerates her? What force acts after her feet are no longer in contact with the ground?What is the reaction force to an action force of 1000 N exerted by Earth on an orbiting communications satellite?If action equals reaction, why isnt Earth pulled into orbit around a communications satellite?A small car bumps into a van at rest in a parking lot. Upon which vehicle is the force of impact greater? Which vehicle undergoes the greater change in acceleration? Defend your answer.Does your answer to question 36 depend on the relative speeds of the vehicles?A speeding bus makes contact with a bug that splatters onto the windshield. Because Of the sudden force, the unfortunate bug undergoes a sudden deceleration. Is the corresponding force that the bug exerts against the windshield greater, less, or the same? Is the resulting deceleration of the bus greater than, less than, or the same as that of the bug?Consider two carts, one twice as massive as the other, that fly apart when the compressed spring squeezed between them is released. How fast does the heavier cart roll compared with the lighter cart?Some people used to think that a rocket could not travel to the moon because it would have no air to push against once it left Earths atmosphere. We now know that idea was mistaken. What force propels a rocket when it is in a vacuum?Since the force that acts on a cannonball when a cannon is fired is equal and opposite to the force that acts on the cannon, does this imply a zero net force and therefore the impossibility of an accelerating cannonball? Explain.Suppose you exert 200 N on your refrigerator and push it across the kitchen floor at constant velocity. What friction force acts between the refrigerator and the floor? Is the friction force equal and opposite to your 200-N push? Does the friction force make up the reaction force to your push?The photo shows Steve Hewitt and his daughter Gretchen. Is Gretchen touching Steve, or is Steve touching her? Explain.Hold your hand like a flat wing outside the window of a moving vehicle. Then tilt it slightly upward and your hand will rise. Explain this in terms of Newtons third law.Your teacher challenges you and your best friend to each pull on a pair of scales attached to the ends of a horizontal rope, in tug-of-war fashion, so that the readings on the scales will differ. Can this be done? Explain.A pair of 50-N weights are attached to a spring scale as shown. Does the spring scale read 0, 50, or 100 N? (Hint: Would it read any differently if one of the strings were held by your hand instead of being attached to the 50-N weight?)The strong man can withstand the tension force exerted by the two horses pulling in opposite directions. How would the tension compare if only one horse pulled and the left rope were tied to a tree? How would the tension compare if the two horses pulled in the same direction, with the left rope tied to the tree?A balloon floats motionless in the air. A balloonist begins climbing up the supporting cable. In which direction does the balloon move as the balloonist climbs? Explain.When you get up from a sitting position, do your feet push against the floor with a force equal to, more than, or less than your weight? Explain.When a weightlifter jerks a barbell over his head, is the force exerted on the barbell more than, less than, or equal to the bar-bells weight? Explain.Identify two pairs of action-reaction forces that exist when you stand on a scale.A car of mass m cruises along the highway at a constant velocity v. The tires push back-ward on the road with a force f. The reaction to this force provides the forward force on the car. Wind resistance against the car is R. a. Using symbols, what is the net force on the car? b. Using symbols, what is the acceleration of the car? c. A friend says that since the car is moving forward, there must be a net forward force, which means f must be greater than R, even at constant velocity. What do you say to enlighten your friend?What will be the acceleration of recoil when a 60-kg person on rollerskates pushes against a wall with a force of 30 N?Two people attempt a tug-of-war on low-friction ice. One person has four times the mass of the other. Relative to the acceleration of the heavier person, what will be the acceleration of the lighter person?Two blocks, one three times as massive as the other, are connected by a compressed spring. When the spring is released, both blocks fly apart. Relative to the acceleration of the heavier block, what is the acceleration of the lighter block?What is the net force on a falling 100-N barrel hitting a pavement with 5000 N of force?Amanda looks at a 1.0-kg bag of jellybeans resting on a table. a. Calculate the amount of force that the table exerts on the bag of jellybeans. b. How does this compare with the force that the bag of jellybeans exerts on the table?When 56-kg Diane on rollerskates pushes against a wall with a force of 28 N, she accelerates away from the wall. Show that Dianes recoil acceleration is 0.50m/s2.A 7.00-kg bowling ball moving at 8.0 m/s strikes a 1.0-kg bowling pin and slows to 7.0 m/s in 0.040 s. a. Show that the force of impact on the bowling ball is 175 N. b. How much force acts on the bowling pin?A 70-kg skydiver is falling at her terminal speed. Show that she exerts a 700-N downward force on the air as she falls.Gymnast Gracie of weight mg is suspended by a pair of vertical ropes attached to the ceiling. a. In terms of Gracies weight, what is the tension in each rope? b. If Gracies mass is 30 kg, show that the tension in each rope is 150 N.Distinguish between mass and momentum. Which is inertia and which is inertia in motion?a. Which has the greater mass, a heavy truck at rest or a roiling Skateboard? b. Which has greater momentum?Distinguish between force and impulse.Distinguish between impact and impulse. Which designates a force and which is force multiplied by time?When the force of impact on an object is extended in time, does the impulse increase or decrease?Distinguish between impulse and momentum. Which is forcetime and which is inertia in motion?Does impulse equal momentum, or a change in momentum?For a constant force, suppose the duration of impact on an object is doubled. a. How much is the impulse increased? b. How much the resulting change in momentum increased?In a car crash, why is it advantageous for an occupant to extend the time during which the collision takes place?If the time of impact in a collision is extended by four times, how much does the force of impact change?Why is it advantageous for a boxer to ride with the punch? Why should he avoid moving into an oncoming punch?Visualize yourself on a skateboard. a. When you throw a balk, do you experience an impulse? b. Do you experience an impulse when you catch a ball of the same speed? c. Do you experience an impulse when you catch it and theu throw it out again? d. Which impulse is greatest?Why is more impulse delivered during a collision when bouncing occurs than during one when it doesnt?Why is the Pelton Wheel an improvement over paddle wheels with flat blades?In terms of momentum conservation, why does a cannon recoil when fired?What does it mean to say that momentum is conserved?Distinguish between an elastic and an inelastic collision.Imagine that you are hovering next to the space shuttle in an Earth orbit. Your buddy of equal mass, who is moving at 4 km/h with respect to the shuttle, bumps into you. If he holds onto you, how fast do you both move with respect to the ship?Is momentum conserved for colliding objects that are moving at angles to one another? Explain.The balls have different masses and speeds. Rank the following from greatest to least. a. momentum b. the impulse needed to stop themBelow are before-and-after pictures of a cars speed. The mass of the car doesnt change. Rank the following from greatest to least. a. the magnitude of momentum change b. the magnitude of the impulse producing the momentum changeJogging Jake runs along a train flatcar that moves at the velocities shown. In each case, Jakes velocity is given relative to the car. Rank the following from greatest to least. a. the magnitude of Jakes momentum relative to the car b. Jakes momentum to the right relative to an observer at rest on the groundRick pushes crates starting at rest across a floor for 3 seconds with a net force as shown. For each crate, rank the following from greatest to least. a. change in momentum b. final speed c. momentum in 3 secondsCalculate the momentum of a 10-kg bowling ball rolling at 2 m/s.Calculate the momentum of a 50-kg carton that slides at 4 m/s across an icy surface. Impulse=FtCalculate the impulse when an average force of 10 N is exerted on a cart for 2.5 s.Calculate the impulse when an average force of 10 N acts on a cart for 5.0 s.A lunar vehicle is tested on Earth at a speed of 10 km/h. When it travels as fast on the moon, is its momentum more, less, or the same?When you ride a bicycle at full speed and the bike stops suddenly, why do you have to push hard on the handlebars to keep from flying forward?Can Andrew produce a net impulse on an automobile by sitting inside and pushing on the dashboard? Can the internal forces within a soccer ball produce an impulse on the soccer ball that will change its momentum?Brian tries to jump from his canoe to the dock. He lands in the water, delighting his companions. Whats your explanation for his mishap?Jason throws a ball horizontally while standing on roller skates. He rolls backward with a momentum that matches that of the ball. Will he end up rolling backward if he goes through the motions of throwing the ball, but does not let go of it? Explain.The example in the previous question can be explained in terms of momentum conservation and in terms of Newtons third law. Assuming you've answered it in terms of momentum conservation, answer it also in terms of Newtons third law (or vice versa if you answered already via Newtons third law).In the previous chapter, rocket propulsion was explained in terms of Newtons third law. That is, the force that propels a rocket is from the exhaust gases pushing against the rocket, the reaction to the force the rocket exerts on the exhaust gases. Explain rocket propulsion in terms of momentum conservation.In terms of impulse and momentum, why are air bags in automobiles a good idea?36AWhen jumping from a significant height, why is it advantageous to land with your knees slightly bent?In terms of impulse and momentum, why are nylon ropes, which stretch considerably under tension, favored by mountain climbers?Would it be a dangerous mistake for a bungee jumper to use a steel cable rather than an elastic cord?When catching a foul ball at a baseball game, why is it important to extend your bare hands upward so they can move downward as the ball is being caught?Why would it be a poor idea to have the back of your hand up against the outfield wall when you catch a long fly ball?42AWhy is it difficult for a firefighter to hold a hose that ejects large amounts of water at high speed?You cant throw a raw egg against a wall without breaking the shell, but you can throw it at the same speed into a sagging sheet without breaking it. Explain.Why can Muhammad exert a greater punching force with his bare fist than he can while wearing a boxing glove?Why do 6-ounce boxing gloves hit harder than 16-ounce gloves?Suppose you roll a bowling ball into a pillow and the ball stops. Now suppose you roll it against a spring and it bounces back with an equal and opposite momentum. a. Which object exerts a greater impulse, the pillow or the spring? b. If the time it takes the pillow to stop the ball is the same as the time of contact of the ball with the spring, how do the average forces exerted on the ball compare?If you topple from your treehouse, you'll continuously gain momentum as you fall to the ground below. Doesnt this violate the law of conservation of momentum? Defend your answer.If a fully loaded shopping cart and an empty one traveling at the same speed have a head-on collision, which cart will experience the greater force of impact? The greater impulse? The greater change in momentum? The greater acceleration?A bug and the windshield of a fast-moving car collide. Indicate whether each of the following statements is true or false. a. The forces of impact on the bug and on the car are the same size. b. The impulses on the bug and on the car are the same size. c. The changes in speed of the bug and of the car are the same. d. The changes in momentum of the bug and of the car are the same size.What difference in recoil would you expect in firing a solid ball versus firing a hollow ball from the same cannon? Explain.A group of playful astronauts, each with a bag full of balls, form a circle as they free-fall in space. Describe what happens when they begin tossing balls simultaneously to one another.A proton from an accelerator strikes an atom. An electron is observed flying forward in the same direction the proton was moving and at a speed much greater than the speed of the proton. What conclusion can you draw about the relative mass of a proton and an electron?Using units, show that kgm/s is equivalent to Ns.A 1000-kg car moving at 20 m/s slams into a building and comes to a halt. Which of the following questions can be answered using the given information, and which one cannot be answered? Explain. a. What impulse acts on the car? b. What is the force of impact on the car?A car with a mass of 1000 kg moves at 20 m/s. What braking force is needed to bring the car to a halt in 10 s?A 2-kg blob of putty moving at 3 m/s slams into a 2-kg blob of putty at rest. a. Calculate the speed of the two stuck-together blobs of putty immediately after colliding. b. Calculate the speed of the two blobs if the one at rest was 4 kg.A 1-kg dart moving horizontally at 10 m/s strikes and sticks to a wood block of mass 9 kg, which slides across a friction-free level surface. What is the speed of the block and the dart after the collision?Assume an 8-kg bowling ball moving at 2 m/s bounces off a spring at the same speed that it had before bouncing. a. What is its momentum of recoil? b. What is its change in momentum? (Hint: What is the change in temperature when something goes from 1 to 1?) c. If the interaction with the spring occurs in 0.5 s, calculate the average force the spring exerts on it.Brakes are applied in bringing a 1200-kg car moving at 25 m/s to rest in 20.0 s. Show that the amount of braking force is 1500 N.A 20.0-kg mass moving at a speed of 3.0 m/s is stopped by a constant force of 15.0 N. Show that the stopping time required is 4.0 s.A 1-kg ostrich egg is thrown at 2 m/s at a bed sheet and is brought to rest in 0.2 s. Show that the average amount of force on the egg is 10 N.A railroad diesel engine weighs four times as much as a freight car. If the diesel engine coasts at 5 km/h into a freight car that is at rest, how fast do the two coast after they couple?A comic-strip superhero meets an asteroid in outer space and hurls it at 100 m/s. The asteroid is a thousand times more massive than the superhero is. In the strip, the superhero is seen at rest after the throw. Taking physics into account, what would be his recoil speed? What is this in miles per hour?A 5-kg fish swimming I m/s swallows an absent-minded 1-kg fish at rest. What is the speed of the large fish immediately after lunch? What would its speed be if the small fish were swimming toward it at 4 m/s?A force sets an object in motion. When the force is multiplied by the time of its application, we call the quantity impulse, which changes the momentum of that object. What do we call the quantity forcedistance, and what quantity can this change?Work is required to lift a barbell. How many times more work is required to lift the bar-bell three times as high?Which requires more work, lifting a 10-kg load a vertical distance of 2 m or lifting a 5-kg load a vertical distance of 4 m?How many joules of work are done on an object when a force of 10 N pushes it a distance of 10 m?How much power is required to do 100 J of work on an object in a time of 0.5 s? How much power is required if the same work is done in 1 s?What are the two main forms of mechanical energy?7AA boulder is raised above the ground so that its potential energy relative to the ground is 200 J. Then it is dropped. What is its kinetic energy just before it hits the ground?Suppose you know the amount of work the brakes of a car must do to stop a car at a given speed. How much work must they do to stop a car that is moving four times as fast? How will the stopping distances compare?How does speed affect the friction between a road and a skidding tire?What will be the kinetic energy of an arrow having a potential energy of 50 J after it is shot from a bow?What does it mean to say that in any system the total energy score stays the same?In what sense is energy from coal actually solar energy?How does the amount of work done on an automobile by its engine relate to the energy content of the gasoline?In what two ways can a machine alter an input force?In what way is a machine subject to the law of energy conservation? Is it possible for a machine to multiply energy or work input?What does it mean to say that a machine has a certain mechanical advantage?In which type of lever is the output force smaller than the input force?What is the efficiency of a machine that requires 100 J of energy to do 35 J of work?Distinguish between theoretical mechanical advantage and actual mechanical advantage. How would these compare if a machine were 100% efficient?What is the efficiency of her body when a cyclist expends 1000 W of power to deliver mechanical energy to the bicycle at the rate of 100 W?In what sense are our bodies machines?23AWhat is the ultimate source of geothermal energy?Can we correctly say that a new source of energy is hydrogen? Why or why not?The mass and speed of three vehicles are shown below. a. Rank the vehicles by momentum from greatest to least. b. Rank the vehicles by kinetic energy from greatest to least.Consider these four situations. (A) a 3-kg ball at rest atop a 5-m-tall hill (B) a 4-kg ball at rest atop a 5-m-tall hill (C) a 3-kg ball moving at 2 m/s atop a 5-m-tall hill (D) a 4-kg ball moving at 2 m/s at ground level a. Rank from greatest to least the potential energy of each ball. b. Rank from greatest to least the kinetic energy of each ball. c. Rank from greatest to least the total energy of each ball.A ball is released at the left end of the metal track shown below. Assume it has only enough friction to roll, but not to lessen its speed. a. Rank from greatest to least the balls momentum at each point. b. Rank from greatest to least the balls kinetic energy at each point. c. Rank from greatest to least the balls potential energy at each point.The roller coaster ride starts with the car at rest at point A. a. Rank from greatest to least the cars speed at each point. b. Rank from greatest to least the cars kinetic energy at each point. c. Rank from greatest to least the cars potential energy at each point.Rank the efficiency of these machines from highest to lowest: (A) energy in 100 J; energy out 60 J (B) energy in 100 J; energy out 50 J (C) energy in 200 J; energy out 80 J (D) energy in 200 J; energy out 120 J31ARank the scale readings from greatest to least. (Ignore friction.)Calculate the work done when a force of 1 N moves a book 2 m.Calculate the work done when a 20-N force pushes a cart 3.5 m.Calculate the work done in lifting a 500-N barbell 2.2 m above the floor. (What is the potential energy of the barbell when it is lifted to this height?) Power=workdonetimeintervalCalculate the watts of power expended when a force of 1 N moves a book 2 m in a time interval of 1 s.Calculate the power expended when a 20-N force pushes a cart 3.5 m in a time of 0.5 s. Gravitationalpotentialenergy=weightheightPE=mghHow many joules of potential energy does a 1-kg book gain when it is elevated 4 m? When it is elevated 8 m? (Let g=10N/kg.)Calculate the increase in potential energy when a 20-kg block of ice is lifted a vertical distance of 2 m.Calculate the number of joules of kinetic energy a 1-kg book has when tossed across the room at a speed of 2 m/s. Work=KEHow much work is required to increase the kinetic energy of a car by 5000 J?What change in kinetic energy does an airplane experience on takeoff if it is moved a distance of 500 m by a sustained net force of 5000 N?Which requires more work: stretching a strong spring a certain distance or stretching a weak spring the same distance? Defend your answer.Two people who weigh the same amount climb a flight of stairs. The first person climbs the stairs in 30 s, while the second person climbs them in 40 s. person does more work? Which uses more power?A physics teacher demonstrates energy conservation by releasing a heavy pendulum bob, as shown in the sketch, allowing it to swing to and fro. What would happen if, in his exuberance, he gave the bob a slight shove as it left his nose? Explain.Consider the kinetic energy of a fly in the cabin of a fast-moving train. Does it have the same or different kinetic energies relative to the train? Relative to the ground outside?When a driver applies brakes to keep a car going downhill at constant speed and constant kinetic energy, the potential energy of the car decreases. Where does this energy go? Where does most of it go in a hybrid vehicle?What is the theoretical mechanical advantage for each of the three lever systems shown?Dry-rock geothermal power can be a major contributor to power with no pollution. The bottom of a hole drilled down into Earths interior is fractured, making a large-surfaced hot cavity. Water is introduced from the top by a second hole. Superheated water rising to the surface then drives a conventional turbine to produce electricity. What is the source of this energy?A stuntman on a cliff has a PE of 10,000 J. Show that when his potential energy is 2000 J, his kinetic energy is 8000 J.Relative to the ground below, how many joules of PE does a 1000-N boulder have at the top of a 5-m ledge? If it falls, with how much KE will it strike the ground? What will be its speed on impact?A hammer falls off a rooftop and strikes the ground with a certain KE. If it fell from a roof that was four times higher, how would its KE of impact compare? Its speed of impact? (Neglect air resistance.)A car can go from 0 to 100 km/h in 10 s. If the engine delivered twice the power, how many seconds would it take?If a car traveling at 60 km/h will skid 20 m when its brakes lock, how far will it skid if it is traveling at 120 km/h when its brakes lock? (This question is typical on some drivers license exams.)Place a small rubber ball on top of a basketball and drop them together. How high does the smaller ball bounce? (Perhaps this is best done in the gym, or outdoors.) Can you reconcile this result with energy conservation?Distinguish between a rotation and a revolution.Does a child on a merry-go-round revolve or rotate around the merry-go-rounds axis?Distinguish between linear speed and rotational speed.What is linear speed called when something moves in a circle?At a given distance from the axis, how does linear (or tangential) speed change as rotational speed changes?At a given rotational speed, how does linear (or tangential) speed change as the distance from the axis changes?When you roll a cylinder across a surface it follows a straight-line path. A tapered cup rolled on the same surface follows a circular path. Why?When you whirl a can at the end of a string in a circular path, what is the direction of the force that acts on the can?Does an inward force or an outward force act on the clothes during the spin cycle of an automatic washer?When car makes a turn, do seat belts provide you with a centripetal force or centrifugal force?If the string that holds a whirling can in its circular path breaks, what causes the can to move in a straight-line path—centripetal force, centrifugal force, or a lack of force? What law of physics supports your answer?Identify the action and reaction forces in the interaction between the ladybug and the whirling can in Figure 10.17.A ladybug in the bottom of a whirling tin can feels a centrifugal force pushing it against the bottom of the can. Is there an outside source of this force? Can you identify this as the action force of an action-reaction pair? If so, what is the reaction force?Why is the centrifugal force the ladybug feels in the rotating frame called a fictitious force?Three locations on our rotating world are shown. Rank these locations from greatest to least for the following quantities. a. rotational speed about Earths polar axis b. tangential speedBiker Bob rides his bicycle inside the rotating space station at the speeds and directions given. The tangential speed of the floor of the station is 10 m/s clockwise. a. Rank his speeds from highest to lowest relative to the stars. b. Rank the normal forces on Bob from largest to smallest.Inside Biker Bobs space station is a ladder that extends from the inner surface of the rim to the central axis. Bob climbs the ladder (toward the center). Point A is at the floor, point B is halfway to the center, and point C is at the central axis. a. Rank the linear speeds of Bob relative to the center of the station, from highest to lowest. Or are the speeds the same at all parts of the ladder? b. Rank the support forces Bob experiences on the ladder rungs, from greatest to least. Or are the support forces the same in all locations?The three cups shown below are rolled on a level surface. Rank the cups by the amount they depart from a straight-line path (most curved to least curved).Three types of rollers are placed on slightly inclined parallel meter stick tracks, as shown below. Rank the rollers, in terms of their ability to remain stable as they roll, from greatest to least.A meterstick is mounted horizontally above a turntable as shown. Identical metal washers are hung at the positions shown. The turntable and meterstick are then spun. Rank from greatest to least, the following quantities for the washers. a. rotational speed b. linear speed c. angle the string makes with the vertical d. inward force on each e. outward force on eachA ball is swung in a horizontal circle as shown below. The ball swings from various lengths of rope at the speeds indicated. Rank the tension m the ropes from greatest to least.Paula flies a loop-the-loop maneuver at constant speed. Two forces act on Paula, the force due to gravity and the normal force of the seat pressing on her (which provides the sensation of weight). Rank from largest to smallest the normal forces on Paula at points A, B, and C.A string is used to whirl a 2-kg toy in a horizontal circle of radius 2.5 m. Show that when the toy moves at 3 m/s the tension in the string (the centripetal force) is 7.2 N.A 60-kg ice skater moving at 5 m/s grabs a 6-m rope and is swept into a circular path. Find the tension in the rope.A 2-kg iron ball is swung in a horizontal circular path at the end of a 1.6-m length of rope. Assume the rope is very nearly horizontal and the balls speed is 10 m/s. Calculate the tension in the rope.A 70-kg person sits on the edge of a horizontal rotating platform 2 m from the center of the platform and has a tangential speed of 3 m/s. Calculate the force of friction that keeps the person in place.Dan and Sue cycle at the same speed. The tires on Dans bike are larger in diameter than those on Sues bike. Which wheels, if either, have the greater rotational speed?A large wheel is coupled to a wheel with half the diameter as shown. a. How does the rotational speed of the smaller wheel compare with that of the larger wheel? b. How do the tangential speeds at the rims compare (assuming the belt doesnt slip)?Use the equation =r to explain why the end of a fly swatter moves much faster than your wrist when swatting a fly.The wheels of railroad trains are tapered, a feature especially important on curves. For sharp curves, should the wheels be less tapered or more tapered?If you lose your grip on a rapidly spinning merry-go-round and fall off, in which direction will you fly?Consider the pair of cups taped together as shown. Will this design correct its motion and keep the pair of cups on the track? Predict before you try it and see!Which state in the United States has the greatest tangential speed as Earth rotates around its axis?The speedometer in a car is driven by a cable connected to the shaft that turns the cars wheels. Will speedometer readings be more or less than actual speed when the cars wheels are replaced with smaller ones?Keeping in mind the concept from the previous question, a taxi driver wishes to increase his fares by adjusting the size of his tires. Should he change to larger tires or smaller tires?A motorcyclist is able to ride on the vertical wall of a bowl-shaped track, as shown. Does centripetal force or centrifugal force act on the motorcycle? Defend your answer.When a soaring eagle turns during its flight, what is the source of the centripetal force acting on it?A car resting on a level road has two forces acting on it: its weight (down) and the normal force (up). Recall from Chapter 4 that the normal force is the support force, which is always perpendicular to the supporting surface. If the car makes a turn on a level road, the normal force is still straight up. Friction between the wheels and road is the only centripetal force providing curved motion. Suppose the road is banked so the normal force has a component that provides centripetal force as shown in the sketch. Do you think the road could be banked so that for a given speed and a given radius of curvature, a vehicle could make the turn without friction? Explain.Friction is needed for a car rounding a curve. But if the road is banked, friction may not be required at all. What, then, supplies the needed centripetal force?Under what conditions could a car remain on a banked track covered with slippery ice?A racing car on a flat circular track needs friction between the tires and the track to maintain circular motion. How much more friction is required for twice the speed?Can an object move along a curved path if no force acts on it?When you are in the front passenger seat of a car turning left, you may find that you feel pressed against the right door. Why do you press against the door? Does the door press on you? Does your explanation involve a centrifugal force or Newtons laws?As a car speeds up when rounding a curve, does centripetal acceleration also increase? Use an equation to defend your answer.45AThe sketch shows a coin at the edge of a turntable. The weight of the coin is shown by the vector W. Two other forces act on the coin, the normal force and a force of friction. The friction force prevents the coin from sliding off the edge. Draw in force vectors for both of these.The sketch shows a conical pendulum. The bob swings in a circular path. The tension T and weight W are shown by vectors. Draw a parallelogram with these vectors and show that their resultant lies in the plane of the circle (recall the parallelogram rule in Chapter 5). What name do we use for this resultant force?Consider a bicycle that has wheels with a circumference of 2 m. Solve for the linear speed of the bicycle when its wheels rotate at 1 revolution per second.Solve for the tangential speed of a passenger on a Ferris wheel that has a radius of 10 m and rotates once in 30 s.50AMegan rides a horse at the outer edge of a merry-go-round. She is located 6 m from the central axis and is a bit frightened of the speed. So her parents place her on a horse 3 m from the axis. While on the inner horse, how will her linear speed compare with her speed on the outer horse?Emily rides on a horizontal rotating platform of radius r at an amusement park and moves at speed one-third the way from the center to the outer edge. a. If the rotation rate of the platform remains constant, what will be her linear speed when she moves to the outer edge? b. If Emilys linear speed was 1.0 m/s at one-third the radius from the center; show that she would move at 3.0 m/s at the outer edge.From the equation F=mv2r, calculate the tension in a 2-m length of string that whirls a 1-kg mass at 2 m/s in a horizontal circle.Answer the previous question for each of the following cases. a. twice the mass b. twice the speed c. twice the length of string (radial distance) d. twice the mass, twice the speed, and twice the distance all at the same timeA turntable that turns 10 revolutions each second is located on top of a mountain. Mounted on the turntable is a laser that emits a bright beam of light. As the turn-table and laser rotate, the beam also rotates and sweeps across the sky. On a dark night the beam reaches some clouds 10 km away. a. How fast does the spot of laser light sweep across the clouds? b. How fast does the spot of laser light sweep across clouds that are 20 km away? c. At what distance will the laser beam sweep across the sky at the speed of light (300,000 km/s)?Harry Hotrod rounds a corner in his sports car at 50 km/h. Fortunately, a force of friction holds him on the road. If he rounds the corner at twice the speed, how much greater must the force of friction be to prevent him from skidding off the road? (You can solve this by using a simple proportion.)How does torque differ from force?In what direction should a force be applied to produce maximum torque?How do clockwise and counterclockwise torques compare when a system is balanced?For two kids of different masses balancing on a seesaw, should the heavier kid sit closer or farther from the fulcrum compared with the lighter kid?What part of an object follows a smooth path when the object is made to spin through the air or across a flat smooth surface?6ATo kick a football so that it doesnt rotate through the air, where should it be kicked relative to its center of mass?Describe the motion of the center of mass of a fireworks projectile, before and after it explodes in midair.9AWhere is the center of gravity of an object that hangs in equilibrium? For an object that stands in equilibrium?11AHow far can an object be tipped before it topples over?In terms of center of gravity, support base, and torque, why can you not stand with your heels and back to a wall and then bend over to touch your toes and return to your stand-up position?14ADistinguish between unstable, stable, and neutral equilibrium.Is the gravitational potential energy more, less, or unchanged when the CG of an object is raised?17AWhat accounts for the stability of the Space Needle in Seattle?19AYou hold a meterstick with the same suspended masses at the angles shown. Rank the torque needed to keep the stick steady from largest to smallest.In a physics lab you find four different vertically mounted cart wheels that are not free to rotate. Each has a block that hangs from a string wrapped around the wheel. Rank the torques these blocks produce about the wheel axes from greatest to least.Perky (left) and Sneezlee fright) have the same mass and nicely balance at opposite ends of a seesaw. For the three positions, rank the length of the lever arm between Perky and the center of the seesaw from longest to shortest.When Suzie gradually increases the angle of the incline, the uniform blocks of wood begin to topple (there is enough friction to keep them from sliding). Rank the order in which the blocks tip from first to last.Three people stand with their backs against a wall. They are all agile and in good physical condition. Their task is to lean over and touch their toes without toppling over. Rank their chances for success from highest to lowest.a. Calculate the individual torques produced by the weights of the girl and boy on the seesaw in the figure. What is the net torque? b. Calculate the distance a 600-N boy should sit from the fulcrum. c. Calculate the distance a 300-N girl should sit when the boy weighs 400 N.Which is better for prying open a stuck cover from a can of paint—a screwdriver with a thick handle or one with a long handle? Which is better for turning stubborn screws? Explain.The spool is pulled in three ways, as shown below. There is sufficient friction for rotation. In what direction will the spool roll in each case?If you know your own weight and have seesaw and a meterstick available, how can you determine the approximate weight of a friend?Is the net torque changed when a partner on a seesaw stands or hangs from her end instead of sitting? (Does the lever arm change?)You cannot stand with your heels and back to the wall and then lean over and touch your toes without toppling. Would either stronger legs or longer feet help you to do this? Defend your answer.Explain why a long pole is more beneficial to a tightrope walker if the pole droops.When a bowling ball leaves your hand it may not spin. But farther along the alley it does spin. What produces the spinning?Using the ideas of torque and center of gravity, explain why a ball rolls down a hill.How do you throw a football so that it spins about its long axis when traveling through the air?When you pedal a bicycle, maximum torque is produced when the pedal sprocket arms are in the horizontal position, and no torque is produced when they are in the vertical position. Explain.To balance automobile wheels, particularly when tires have worn unevenly, lead weights are fastened to their edges. Where should the CG of the balanced wheel be located?Why does a washing machine vibrate violently if the clothes are not evenly distributed in the tub?A bottle rack that seems to defy common sense is shown in the figure. Where is the CG of the rack and bottle?Which glass in the figure is unstable and will topple?40AHow can the three bricks in the figure be stacked so that the top brick has maximum horizontal overhang above the bottom brick? For example, stacking them as the dotted lines suggest would be unstable and the bricks would topple. (Hint: Start with the top brick and think your way down. At every interface the CG of the bricks above must not extend beyond the end of the supporting brick.)Why is the middle seating most comfortable in a bus traveling along a bumpy road?43AWhy is it easier to carry the same amount of water in two buckets, one in each hand, than in a single bucket?A long track balanced like a seesaw supports a golf ball and a more massive billiard ball with a compressed spring between the two as shown in the figure. The CG of the two-ball system is therefore directly above the point of support (the triangular fulcrum). When the spring is released, the balls move away from each other. As the balks roll outward, will the track remain in balance, or will it tip? What principles do you use for your explanation?How does a heavy tail enable a monkey standing on a branch to reach to farther branches?Where is the center of mass of Earths atmosphere?As of 2007 more than 225 planets outside our solar system have been found (including an Earthlike one, not too hot and not too cold, likely with liquid water, orbiting about the star Gliese 581). Most of these planets were discovered by tiny wobbles of their parent stars. Why do stellar wobbles indicate the presence of planets?To tighten a bolt, you push with a force of 80 N at the end of a wrench handle that is 0.25 m from the axis of the bolt. a. What torque are you exerting? b. If you move your hand inward to be only 0.10 m from the bolt, what force do you have to exert to achieve the same torque? c. Do your answers depend on the direction of your push relative to the direction of the wrench handle?The diagram below shows a ruler balanced with the fulcrum at the 50-cm mark. Copy the diagram onto a sheet of paper and answer Questions 50-52 below. If a 200-g mass is placed at the 20-cm mark (30 cm from the fulcrum), at what mark should a 500-g mass be placed So that the system balances?The diagram below shows a ruler balanced with the fulcrum at the 50-cm mark. Copy the diagram onto a sheet of paper and answer Questions 50-52 below. If a 100-g mass was placed at the 25-cm mark, and a 20-g mass at the 10-cm mark, where should a 500-g mass be placed to balance the system?The diagram below shows a ruler balanced with the fulcrum at the 50-cm mark. Copy the diagram onto a sheet of paper and answer Questions 50-52 below. Find an arrangement of a 50-g, a 100-g, a 200-g, and a 500-g mass that balances. Show all the calculations and indicate the positions the masses should occupy (as in Questions 50 and 51).The rock has a mass of 1 kg. What is the mass of the measuring stick if it is balanced by a support force at the one-quarter mark?Suspend a belt from a piece of stiff wire that is bent as shown. Why does the belt balance as it does?Hang a hammer on a loose ruler as shown. Then explain why it doesnt fall.What is the law of inertia for rotation?Does the rotational inertia of an object differ for different axes of rotation?Which is easier to get swinging, a baseball bat held at the end, or one held closer to the massive end (choked up)?Which has a greater rotational inertia, a cylinder about its axis or a sphere about a diameter if the two have the same mass and radius?Which will swing to and fro more often, a short pendulum or a long pendulum?Why does bending your legs when running enable you to swing your legs to and fro more rapidly?What are the three principal axes of rotation for the human body?How does a skater decrease his or her rotational inertia while spinning?Which will have the greater acceleration rolling down an incline—a hoop or a solid disk?Distinguish between linear momentum and angular momentum.The text says that angular momentum is 10, then says it is mvr. Which is it?Momentum is conserved when there is no net external force. When is angular momentum conserved?What does it mean to Say that angular momentum is conserved?If a skater who is spinning pulls her arms in so as to reduce her rotational inertia to half, by how much will her angular momentum increase?If a skater who is spinning pulls her arms in so as to reduce her rotational inertia to half, by how much will her rate of spin increase?Why are your answers different to the previous two questions?How can gravity be simulated in an orbiting space station?How will the value of g vary at different distances from the hub of a rotating space station?Three iron shapes of the same mass rotate about the axis shown by the circle with the dot inside. Rank them, from greatest to least, in terms of the rotational inertia about this axis.Beginning from a rest position, a solid disk A, a solid ball B, and a hoop C, race down an incline. Rank them in order of finishing: winner, second place, and third place.Perky rides at different radial distances from the center of a turntable that rotates at a fixed rate. His distances and tangential speeds at three different locations are as follows. (A) r=15cm,v=7.5cm/s (B) r=10cm,v=7.5cm/s (C) r=5.0cm,v=2.5cm/s a. Rank from greatest to least, Perkys angular momenta. b. Rank from greatest to least, the amounts of friction needed to keep Perky from sliding off.Students Art, Bart, Cis, and Dot sit on a rotating turntable at different distances from the center as indicated. (A) Art, m=60kg, sits at 14r. (B) Bart, m=25kg, sits at 12r. (C) Cis, m=50kg, sits at 34r. (D) Dot, m=20kg, sits at r. From greatest to least, rank the angular momenta of the four students.Mei Fan says that a basketball has greater rotational inertia than a solid ball of the same size and mass because most of a basketballs mass is far from its center. Ashley says no, that the center of mass of any uniform ball is at its center, and mass distribution doesnt matter. Whom do you agree with?Stand two metersticks against the wall and let them topple over. Now put a wad of clay on top of one of the sticks and let them topple again. Which reaches the floor first?Why is a stick with a wad of clay at the top easier to balance on the palm of your hand than an empty stick?26AIf you walked along the top of a fence, why would holding your arms out help you to balance?