MASTERPHYS:KNIGHT'S PHYSICS ACCESS+WKB
4th Edition
ISBN: 9780135245033
Author: Knight
Publisher: PEARSON
expand_more
expand_more
format_list_bulleted
Concept explainers
Videos
Textbook Question
Chapter 8, Problem 55EAP
The physics of circular motion sets an upper limit to the speed of human walking. (If you need to go faster, your gait changes from a walk to a run.) If you take a few steps and watch what’s happening, you’ll see that your body pivots in circular motion over your forward foot as you bring your rear foot forward for the next step. As you do so, the normal force of the ground on your foot decreases and your body tries to “lift off’ from the ground.
a. A person’s center of mass is very near the hips, at the top of the legs. Model a person as a particle of mass m at the top of a leg of length L. Find an expression for the person’s maximum walking speed vmax.
b. Evaluate your expression for the maximum walking speed of a 70 kg person with a typical leg length of 70 cm. Give your answer in both m/s and mph, then comment, based on your experience, as to whether this is a reasonable result. A “normal” walking speed is about 3 mph.
Expert Solution & Answer
Want to see the full answer?
Check out a sample textbook solution
Students have asked these similar questions
In deep space, an astronaut is whipping a heavy tool around in a circle by a
taut cable. The cable is 1 meter long (from the astronaut's fist to the tool),
and the tool makes a full trip around the circle in half a second as it moves
with constant speed. The mass of the tool is 10 kg. What is the tension in
the cable?
A stone has a mass of 8.79 g and is wedged into the tread of an automobile tire, as the drawing shows. The coefficient of static friction between the stone and each side of the tread channel is 0.818. When the tire surface is rotating at 10.9m/s, the stone flies out the tread. The magnitude FN of the normal force that each side of the tread channel exerts on the stone is 2.46 N. Assume that only static friction supplies the centripetal force, and determines the radius r of the tire (in terms of m)
A cow is pushing its baby from side of the farm to another. The floor of the farm is not frictionless. The baby has a mass of 3 kg and the cow is carefully pushing it at a constant speed of 0.5 m/s to ensure that it doesn't tip over. What is the net force acting on the baby?
Chapter 8 Solutions
MASTERPHYS:KNIGHT'S PHYSICS ACCESS+WKB
Ch. 8 - In uniform circular motion, which of the following...Ch. 8 - A car runs out of gas while driving down a hill....Ch. 8 - FIGURE Q8.3 is a bird's-eye view of particles on...Ch. 8 - Tarzan swings through the jungle on a massless...Ch. 8 - FIGURE Q8.5 shows two balls of equal mass moving...Ch. 8 - Ramon and Sally are observing a toy car speed up...Ch. 8 - A jet plane is flying on a level course at...Ch. 8 - A small projectile is launched parallel to the...Ch. 8 - 9. You can swing a ball on a string in a vertical...Ch. 8 - A golfer starts with the club over her head and...
Ch. 8 - As a science fair project, you want to launch an...Ch. 8 - A 500 g model rocket is on a cart that is rolling...Ch. 8 - A 4.0 × 1010 kg asteroid is heading directly...Ch. 8 - A 55 kg astronaut who weighs 180 N on a distant...Ch. 8 - A 1500 kg car drives around a flat 200-m-diameter...Ch. 8 - A 1500 kg car takes a 50-m-radius unbanked curve...Ch. 8 - A 200 g block on a 50-cm-long string swings in a...Ch. 8 - In the Bohr model of the hydrogen atom, an...Ch. 8 - Suppose the moon were held in its orbit not by...Ch. 8 - 10. A highway curve of radius 500 m is designed...Ch. 8 - It is proposed that future space stations create...Ch. 8 - A 5.0 g coin is placed 15 cm from the center of a...Ch. 8 - Mass m1on the frictionless table of FIGURE EX8.13...Ch. 8 - A satellite orbiting the moon very near the...Ch. 8 - What is free-fall acceleration toward the sun at...Ch. 8 - 16. A 9.4 × 1021 kg moon orbits a distant planet...Ch. 8 - Communications satellites are placed in circular...Ch. 8 - A car drives over the top of a hill that has a...Ch. 8 - The weight of passengers on a roller coaster...Ch. 8 - A roller coaster car crosses the top of a circular...Ch. 8 - The normal force equals the magnitude of the...Ch. 8 - A student has 65-cm-long arms. What is the minimum...Ch. 8 - While at the county fair, you decide to ride the...Ch. 8 - A 500 g ball swings in a vertical circle at the...Ch. 8 - A 500 g ball moves in a vertical circle on a...Ch. 8 - A heavy ball with a weight of 100 N (m = 10.2 kg)...Ch. 8 - A toy train rolls around a horizontal...Ch. 8 - 28. A new car is tested on a 200-m-diameter track....Ch. 8 - An 85,000 kg stunt plane performs a loop-the-loop,...Ch. 8 - Three cars are driving at 25 m/s along the road...Ch. 8 - Derive Equations 8.3 for the acceleration of a...Ch. 8 - 32. A 100 g bead slides along a frictionless wire...Ch. 8 - 33. Space scientists have a large test chamber...Ch. 8 - 34. A 5000 kg interceptor rocket is launched at an...Ch. 8 - Prob. 35EAPCh. 8 - 36. A rocket- powered hockey puck has a thrust of...Ch. 8 - Prob. 37EAPCh. 8 - A 2.0 kg projectile with initial velocity m/s...Ch. 8 - A 75 kg man weighs himself at the north pole and...Ch. 8 - A concrete highway curve of radius 70 m banked at...Ch. 8 - a. an object of mass m swings in horizontal circle...Ch. 8 -
42. You’ve taken your neighbor’s young child to...Ch. 8 - A 4.4-cm-diameter, 24 g plastic ball is attached...Ch. 8 - A charged particle of mass m moving with speed v...Ch. 8 - Two wires are tied to the 2.0 kg sphere shown in...Ch. 8 - Two wires are tied to the 300 g sphere shown in...Ch. 8 - A conical pendulum is formed by attaching a ball...Ch. 8 - The 10 mg bead in FIGURE P8.48 is free to slide on...Ch. 8 - In an old-fashioned amusement park ride,...Ch. 8 - The ultracentrifuge is an important tool for...Ch. 8 - In an amusement park ride called The Roundup,...Ch. 8 - 52. Suppose you swing a ball of mass m in a...Ch. 8 - A 30 g ball rolls around a 40-cm-diameter L-shaped...Ch. 8 - FIGURE P8.54 shows a small block of mass m sliding...Ch. 8 - The physics of circular motion sets an upper limit...Ch. 8 - A 100 g ball on a 60-cm-long string is swung in a...Ch. 8 - A 60 g ball is tied to the end of a 50-cm-long...Ch. 8 - Elm Street has a pronounced dip at the bottom of a...Ch. 8 - 59. A 100 g ball on a 60-cm-long string is swung...Ch. 8 - Scientists design a new particle accelerator in...Ch. 8 - 61. A 1500 kg car starts from rest and drives...Ch. 8 - Prob. 62EAPCh. 8 - 63. A 2.0 kg ball swings in a vertical circle on...Ch. 8 - In Problems 64 and 65 you are given the equation...Ch. 8 - In Problems 64 and 65 you are given the equation...Ch. 8 - Sam (75 kg) takes off up a 50-m-high, 10°...Ch. 8 - In the absence of air resistance, a projectile...Ch. 8 - The father of Example 8.2 stands at the summit of...Ch. 8 - A small bead slides around a horizontal circle at...Ch. 8 - A 500 g steel block rotates on a steel table while...Ch. 8 - If a vertical cylinder of water (or any other...
Knowledge Booster
Learn more about
Need a deep-dive on the concept behind this application? Look no further. Learn more about this topic, physics and related others by exploring similar questions and additional content below.Similar questions
- The figure shows a 2400 kg cable car descending a high hill. A counterweight of mass 2200 kg on the other side of the hill aids the brakes in controlling the cable car's speed. The rolling friction of both the cable car and the counterweight are negligible. How much braking force does the cable car need to descend at constant speed? Counterweight 200 m 30° 20° 2200 N 3300 N 980 N 4400 Narrow_forwardA 670 N student stands in the middle of a frozen pond having a radius of 6.9 m. He is unable to get to the other side because of a lack of friction between his shoes and the ice. To overcome this difficulty, he throws his 2.9 kg physics textbook horizontally toward the north shore at a speed of 6.9 m/s. The acceleration of gravity is 9.81 m/s². How long does it take him to reach the south shore? Answer in units of s.arrow_forwardConsider a 25-kg block on a frictionless inclined plane held in place by a steel cable as shown in the figure. The cable is parallel to the surface of the incline. What is the magnitude of the tension on the steel cable? 25 kg 30° 212 N O 245 N O none of the choices O 123 N O 458 Narrow_forward
- At night while it is dark, a driver inadvertently parks his car on a drawbridge. Some time later, the bridge must be raised to allow a boat to pass through. The coefficients of friction between the bridge and the car's tires are μs=0.820 and μk=0.470. If the bridge attendant sees the car suddenly start to slide and immediately turns off the bridge's motor, what will be the car's acceleration after it has begun to move? (Express your answer in meters per second squared.)arrow_forwardA 5.0 g coin is placed 15 cm from the center of a turntable. The coin has static and kinetic coefficients of friction with the turntable surface of μs = 0.70 and μk = 0.50. The turntable very slowly speeds up. What is the frequency of the rotation of the turntable expressed in revolutions per minute when the coin slides off? Express your answer in revolutions per minute.arrow_forwardA ball of mass m moves along a track in the shape of vertical circular loop. There are 2 forces acting on the ball -- the normal force exerted by track (Ntrack) and gravity (mg). Ignore friction and air resistance. The vectors v (velocity) and a (total acceleration) have an angle ◊ between them, which changes as the ball moves. Check all the answers which are true statements. There may be more than one correct answer! when the ball is on the way up the loop, 0 > 90°º the magnitude of a is always smaller than g, no matter how fast the ball moves 0 = 90° at the "side" points (halfway up the loop) at the bottom of the loop, Ntrack is stronger than mg the ball falls off the track if Ntrack = 0arrow_forward
- A robot with fancy wheels is trained to move in two directions simultaneously. The force in the forward direction is 10 N and the force in the horizontal direction is 8 N. If the robot starts from rest, has a mass of 75 kg and travels for 100 seconds, what is the magnitude of the robot's final displacement?arrow_forwardA spider hangs from the junction formed by three strands of silk, as shown in the figure. The force of tension in each strand pulls at the junction. The net force at the junction is zero. In other words, the resultant of all three force vectors is zero at the junction. The gravitational force on the spider makes it exert a downward force of 0.15 N on the junction. The two sloping strands are perpendicular to each other. We have chosen the x and y axes to be along those strands as shown. The force of the right strand on the junction has magnitude Tx force of the left strand on the junction has unknown magnitude T,y. a) Calculate Ty. b) Calculate the angle between the x axis and the horizontal direction. Hint: The SI unit of force is the newton, which is abbreviated as N. You must consider three force vectors. The x components of all three vectors must add to zero, and the y components must also add to zero. Note that the coordinate system is "rotated" which is Tx Ty 0.127 Ν. The a…arrow_forwardA stacked pair of books with masses m1= 2.0 kg (bottom book) and m2 = 1.5 kg (top book) are tossed onto a table. The books strike the table with no vertical velocity and their common horizontal speed is ?o = 0.75 m/s. The kinetic friction coefficient between the bottom book and the table is ?k1=0.45; the kinetic and static friction coefficients between the two books are ?k2=0.3 and ?s2= 0.4. Find the final horizontal position of each book relative to the spot where the stack hits the table.arrow_forward
- The figure shows a container of mass m1 = 4.4 kg connected to a block of mass m2 by a cord looped around a frictionless pulley. The cord and pulley have negligible mass. When the container is released from rest, it accelerates at 1.3 m/s2 across the horizontal frictionless surface. What are (a) the tension in the cord and (b) mass m2?arrow_forwardOne end of a rope is tied to a 11 kg hanging weight. The rope goes over a pulley and the other end is tied to a 11.7 kg block on flat ground and pulls the block horizontally towards the pulley. The coefficient of kinetic friction is .2. The block is sliding away from the pulley at 3.0 m/s (the weight is being pulled upwards). What is the magnitude of the acceleration of the block in meters per second squared?arrow_forwardThe standing vertical jump is a good test of an athlete’s strength and fitness. The athlete goes into a deep crouch, then extends his legs rapidly; when his legs are fully extended, he leaves the ground and rises to his highest height. It is the force of the ground on the athlete during the extension phase that accelerates the athlete to the final speed with which he leaves the ground. A good jumper can exert a force on the ground equal to twice his weight. If his crouch is 60 cm deep, how far off the ground does he rise?arrow_forward
arrow_back_ios
SEE MORE QUESTIONS
arrow_forward_ios
Recommended textbooks for you
Physics for Scientists and Engineers: Foundations...PhysicsISBN:9781133939146Author:Katz, Debora M.Publisher:Cengage Learning
Principles of Physics: A Calculus-Based TextPhysicsISBN:9781133104261Author:Raymond A. Serway, John W. JewettPublisher:Cengage Learning
Physics for Scientists and Engineers: Foundations...
Physics
ISBN:9781133939146
Author:Katz, Debora M.
Publisher:Cengage Learning
Principles of Physics: A Calculus-Based Text
Physics
ISBN:9781133104261
Author:Raymond A. Serway, John W. Jewett
Publisher:Cengage Learning
Newton's First Law of Motion: Mass and Inertia; Author: Professor Dave explains;https://www.youtube.com/watch?v=1XSyyjcEHo0;License: Standard YouTube License, CC-BY