1. In which one of the following situations is zero net work done? (a) A ball rolls down an inclined plane. (b) A physics student stretches a spring. (c) A projectile falls toward the surface of Earth. (d) A box is pulled across a rough floor at constant velocity. (e) A child pulls a wagon across a rough surface causing it to accelerate.
Kinematics
A machine is a device that accepts energy in some available form and utilizes it to do a type of work. Energy, work, or power has to be transferred from one mechanical part to another to run a machine. While the transfer of energy between two machine parts, those two parts experience a relative motion with each other. Studying such relative motions is termed kinematics.
Kinetic Energy and Work-Energy Theorem
In physics, work is the product of the net force in direction of the displacement and the magnitude of this displacement or it can also be defined as the energy transfer of an object when it is moved for a distance due to the forces acting on it in the direction of displacement and perpendicular to the displacement which is called the normal force. Energy is the capacity of any object doing work. The SI unit of work is joule and energy is Joule. This principle follows the second law of Newton's law of motion where the net force causes the acceleration of an object. The force of gravity which is downward force and the normal force acting on an object which is perpendicular to the object are equal in magnitude but opposite to the direction, so while determining the net force, these two components cancel out. The net force is the horizontal component of the force and in our explanation, we consider everything as frictionless surface since friction should also be calculated while called the work-energy component of the object. The two most basics of energy classification are potential energy and kinetic energy. There are various kinds of kinetic energy like chemical, mechanical, thermal, nuclear, electrical, radiant energy, and so on. The work is done when there is a change in energy and it mainly depends on the application of force and movement of the object. Let us say how much work is needed to lift a 5kg ball 5m high. Work is mathematically represented as Force ×Displacement. So it will be 5kg times the gravitational constant on earth and the distance moved by the object. Wnet=Fnet times Displacement.
Choose the letter of the correct answer. Write the letter in CAPITAL LETTERS.
for questions 2 and 4 the image is attached:
1. In which one of the following situations is zero net work done?
(a) A ball rolls down an inclined plane.
(b) A physics student stretches a spring.
(c) A projectile falls toward the surface of Earth.
(d) A box is pulled across a rough floor at constant velocity.
(e) A child pulls a wagon across a rough surface causing it to accelerate.
2. A concrete block is pulled 7.0 m across a frictionless surface by means of a rope. The tension in the rope is 40 N; and the
net work done on the block is 247 J. What angle does the rope make with the horizontal?
(a) 28° (b) 41° (c) 47° (d) 62° (e) 88°
3. Mike is cutting the grass using a human-powered lawn mower. He pushes the mower with a force of
45 N directed at an angle of 41° below the horizontal direction. Calculate the work that Mike does on
the mower in pushing it 9.1 m across the yard.
(a) 510 J (b) 460 J (c) 410 J (d) 360 J (e) 310 J
4. A constant force of 25 N is applied as shown to a block which undergoes a displacement of 7.5 m to the right along a frictionless surface while the force acts. What is the work done by the force?
(a) zero joules (b) +94 J (c) −94 J (d) +162 J (e) −162 J
5. Which one of the following statements concerning kinetic energy is true?
(a) It can be measured in watts.
(b) It is always equal to the potential energy.
(c) It is always positive.
(d) It is a quantitative measure of inertia.
(e) It is directly proportional to velocity.
6. The kinetic energy of a car is 8 × 106 J as it travels along a horizontal road. How much work is required to stop the car in 10 s?
(a) zero joules (b) 8 × 104 J (c) 8 × 105 J (d) 8 × 106 J (e) 8 × 107 J
7. How much energy is dissipated in braking a 1000-kg car to a stop from an initial speed of 20 m/s?
(a) 20 000 J (b) 200 000 J (c) 400 000 J (d) 800 000 J (e) 10 000 J
8. The kinetic energy of an 1100-kg truck is 4.6 × 105 J. What is the speed of the truck?
(a) 21 m/s (b) 29 m/s (c) 33 m/s (d) 17 m/s (e) 25 m/s
9. A 40-kg block is lifted vertically 20 meters from the surface of the earth. To one significant figure, what is the change in the gravitational potential energy of the block?
(a) +800 J (b) −800 J (c) +8000 J (d) −8000 J (e) zero joules
10. The kinetic energy of a car is 8 × 106 J as it travels along a horizontal road. How much power is required to stop the car in 10 s?
(a) zero watts (b) 8 × 104 W (c) 8 × 105 W (d) 8 × 106 W (e) 8 × 107 W
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