1st Year Physics – 2
A.P. Physics - B Unit 3: Work, Energy, & Momentum
Multiple Choice Practice
1. A plane 5 meters in length is inclined at an angle of 37°, as shown. A block of weight 20 newtons is placed at the top of the plane and allowed to slide down.
[pic]
The work done on the block by the gravitational force during the 5-meter slide down the plane is most nearly
(A) 20 J
(B) 60 J
(C) 80 J
(D) 100 J
(E) 130 J
2. An amount of net work W is done on an object, accelerating it from rest to a final speed v. Then the object is stopped and now an amount of net work 2W is done. How fast is the object moving after the 2W work is done on it?
(A) v/4
(B) v/2
(C) [pic]v
(D) 2v
(E) 4v
[pic]
3. A block of mass 3 kg slides along a horizontal surface that has negligible friction except for one section, as shown above. The block arrives at the rough section with a speed of 5 m/s and leaves it 0.5s later with a speed of 3 m/s. What is the magnitude of the work done by the frictional force exerted on the block by the rough section of the surface?
(A) 24 J
(B) 16 J
(C) 8 J
(D) 6 J
(E) 3 J
4. A block of mass m slides on a horizontal frictionless table with an initial speed vo. It then compresses a spring of force constant k and is brought to rest. How much is the spring compressed from its natural length?
(A) [pic]
(B) [pic]
(C) [pic]
(D) [pic]
(E) [pic]
Questions 5-6:
[pic]
A block released from rest at position A slides with negligible friction down an inclined track, around a vertical loop, and then along a horizontal portion of the track, as shown above. The block never leaves the track.
5. After the block is released, in which of the following sequences of positions is the speed of the block ordered from fastest to slowest?
(A) B C D E
(B) B E C D
(C) D C E B
(D) E B C D
(E) E D C B
6. The gravitational potential energy and the kinetic energy of the block are most nearly equal at which position? (Consider the potential energy to be zero at position B.)
(A) A
(B) B
(C) C
(D) D
(E) E
7. An object is initially sliding down an incline with 700J of KE and 300J of PEg (relative to the base of the incline). During its slide, friction and air resistance both do work on the object. If the magnitude of work done by friction is 200J, and if the object reaches the bottom of the incline with KE of 750J, how much work did air resistance do on the object?
(A) 50 J
(B) 250 J
(C) 300 J
(D) 450 J
(E) 650 J
[pic]
8. The figure above shows a rough semicircular track whose ends are at a vertical height h. A block placed at point P at one end of the track is released from rest and slides past the bottom of the track. Which of the following is true of the height to which the block rises on the other side of the track?
(A) It is equal to h/2(
(B) It is equal to h/4
(C) It is equal to h/2
(D) It is equal to h
(E) It is between zero and h; the exact height depends on how much energy is lost to friction.
9. A weight lifter lifts a mass m at constant speed to a height h in time t. What is the average power output of the weight lifter?
(A) mg
(B) mh
(C) mgh
(D) mght
(E) mgh /t
10. A horizontal force F is used to pull a 5 kg block across a floor at a constant speed of 3 m/s. The frictional force between the block and the floor is 10 newtons. The work done by the force F in 1 minute is most nearly
(A) 0 J
(B) 30 J
(C) 600 J
(D) 1,350 J
(E) 1,800 J
11. A ball of mass m and momentum p has kinetic energy equal to which of the following?
(A) [pic][pic]
(B) [pic]
(C) [pic]
(D) [pic]
(E) [pic]
12. A force of constant magnitude F and fixed direction acts on an object of mass m that is initially at rest. If the force acts for a time interval (t over a displacement (x, what is the magnitude of the resultant change in the linear momentum of the object?
(A) F(t
(B) F(x
(C) F(t / m
(D) F(x / m
(E) mF(t
13. Two bodies of masses 5 and 7 kilograms are initially at rest on a horizontal frictionless surface. A light spring is compressed between the bodies, which are held together by a thin thread. After the spring is released by burning through the thread, the 5 kilogram body has a speed of 0.2 m/s. The speed of the 7 kilogram body (in m/s) is
(A) [pic]
(B) [pic]
(C) [pic]
(D) [pic]
(E) [pic]
[pic]
14. A railroad car of mass m is moving with speed v when it collides with and connects to a second railroad car of mass 3m, initially at rest, as shown above. How do the speed and kinetic energy of the connected cars compare to those of the single car of mass m before the collision?
Speed Kinetic Energy
(A) Less Less
(B) Less The same
(C) The same Less
(D) The same The same
(E) Greater The same
16. Two objects having the same mass travel toward each other on a flat surface, each with a speed of 1 m/s relative to the surface. The objects collide head-on and are reported to rebound after the collision, each with a speed of 2 m/s relative to the surface. Which of the following assessments of this report is most accurate?
(A) Momentum was not conserved, therefore the report is false.
(B) If potential energy was released to the objects during the collision, the report could be true.
(C) If the objects had different masses, the report could be true.
(D) If the surface was inclined, the report could be true.
(E) If there was no friction between the objects and the surface, the report could be true.
15. Two skaters are initially at rest next to each other on frictionless ice. Skater A pushes on skater B. If skater A has greater mass than skater B, which of the following correctly relates the magnitudes of their momentums p and their kinetic energies K after the push?
(A) pA = pB and KA < KB
(B) pA = pB and KA = KB
(C) pA = pB and KA > KB
(D) pA < pB and KA < KB
(E) pA < pB and KA = KB
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