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Chapter 5 & 6.3 review

Momentum and Collisions

Write the letter of the correct answer in the space provided.

_______ 1. Two cars collide, lock bumpers, and move together after the collision. What kind of collision is this?a. elastic collisionb. inelastic collisionc. perfectly elastic collisiond. perfectly inelastic collision

_______ 2. A tennis ball is dropped from 1.0 m, bounces off the ground, and rises to 0.85 m. What kind of collision occurred between the ball and the ground?a. elastic collisionb. inelastic collisionc. perfectly elastic collisiond. perfectly inelastic collision

_______ 3. In what kind of collision is kinetic energy always conserved?a. elastic collisionb. inelastic collisionc. perfectly elastic collisiond. perfectly inelastic collision

_______ 4. Most collisions in the everyday world area. elastic collisions.b. inelastic collisions.c. perfectly elastic collisions.d. perfectly inelastic collisions.

_______ 5. When an inelastic material is in a collision,a. the work done to deform the material is equal to the work done to return the material to its original shape.b. the work done to deform the material is equal to the work the material does to other objects in the

collision.c. the work done to deform the material is equal to the increase in the system’s total kinetic energy.d. some of the work done to deform the material is converted to other forms of energy.

_______ 6. A helium atom collides with another helium atom in an elastic collision. Which of the following is true?a. Both momentum and kinetic energy are conserved.b. Momentum is conserved but kinetic energy is not conserved.c. Kinetic energy is conserved but momentum is not conserved.d. Neither momentum nor kinetic energy is conserved.

_______ 7. Two playground balls collide in an inelastic collision. Which of the following is true?a. Both momentum and kinetic energy are conserved.b. Momentum is conserved, but kinetic energy is not conserved.c. Kinetic energy is conserved, but momentum is not conserved.d. Neither momentum nor kinetic energy is conserved.

_______ 8. Two balls of dough collide and stick together. Identify the type of collision.a. elastic c. inelasticb. perfectly elastic d. perfectly inelastic

_______ 9. Which of the following is not evidence that kinetic energy has been lost in a collision?a. The collision produces a sound.b. At least one of the objects is deformed after the collision.c. At least one of the objects increases in temperature as a result of the collision.d. One of the objects is at rest after the collision.

____ 10. Two objects with different masses collide and bounce back after an elastic collision. Before the collision, the two objects were moving at velocities equal in magnitude but opposite in direction. After the collision:

a. the less massive object had gained momentum.b. the more massive object had gained momentum.c. both objects had the same momentum.d. both objects lost momentum.

_______11. Which of the following best describes the momentum of two bodies after a two-body collision if the kinetic energy of the system is conserved?a. must be less c. might also be conservedb. must also be conserved d. is doubled in value

_______12. A worker does 25 J of work lifting a bucket, then sets the bucket back down in the same place. What is the total net work done on the bucket?a. 25 J c. 25 Jb. 0 J d. 50 J

_______13. If both the mass and the velocity of a ball were tripled, the kinetic energy of the ball would increase by a factor ofa. 3. c. 9.b. 6. d. 27.

_______14. What is the kinetic energy of a 0.135 kg baseball thrown at 40.0 m/s?a. 54.0 J c. 108 Jb. 87.0 J d. 216 J

_______15. If friction is the only force acting on an object during a given physical process, which of the following assumptions can be made in regard to the object’s kinetic energy?a. The kinetic energy decreases.b. The kinetic energy increases.c. The kinetic energy remains constant.d. The kinetic energy decreases and then increases.

_______16. The equation for determining gravitational potential energy isPEg = mgh. Which factor(s) in this equation is (are) not intrinsic to an object?a. m c. hb. g d. both g and h

_______17. Which of the following parameters does not depend on how resistant a spring is to being compressed or stretched?a. compression distance c. spring constantb. relaxed length d. stretching distance

_______18. What is the potential energy of a 1.0 kg mass 1.0 m above the ground?a. 1.0 J c. 10 Jb. 9.8 J d. 96 J

_____ 19. Can an object have negative energy? If yes, what form of energy does it come from?

a. No b. Yes, KE c. Yes, PEg d. Yes, PEelastic e. Yes, other

_______20. Why doesn’t the principle of mechanical energy conservation hold in situations when frictional forces are present?a. Kinetic energy is not completely converted to a form of potential energy.b. Potential energy is completely converted to a form of gravitational energy.c. Chemical energy is not completely converted to electrical energy.d. Kinetic energy is completely converted to a form of gravitational energy.

_______21. For which of the following situations is the conservation of mechanical energy most likely to be a valid assumption?a. A skateboard rolls across a sewer grate.b. A parachutist falls from a plane.c. You rub your hands together to keep warm.d. A soccer ball flies through the air.

_______22. A 3.00 kg toy falls from a height of 1.00 m. What will the kinetic energy of the toy be just before the toy hits the ground? (Assume no air resistance and that g = 9.81 m/s2.)a. 98.0 J c. 29.4 Jb. 0.98 J d. 294 J

_______23. What is the average power supplied by a 60.0 kg person running up a flight of stairs a vertical distance of 4.0 m in 4.2 s?a.57 W c. 560 Wb.240 W d. 670 W

____ 24. A Watt is equivalent to which of the following quantities?

a. kgm/s3 b. kgm/s2 c. kgm/s d. kg(m/s)2 e. none of these

____ 25. Gravitational potential energy is always measured in relation to:

a. an arbitrary zero level b. total potential energyc. where mechanical energy is conserved d. half of the kinetic energy

____ 26. If rain falls at a rate of 50 g/s and then falls for 750 m, on average, how much power is generated by the falling rain?a. 367.5 kW b. 37.5 W c. 37.5 kW d. 367.5 W

____ 27. Why doesn’t the principle of mechanical energy conservation hold in situations when frictional forces are present?

a. Kinetic energy is not completely converted to a form of potential energy.b. Potential energy is completely converted to a form of gravitational energy.c. Chemical energy is not completely converted to electrical energy.d. Kinetic energy is completely converted to a form of gravitational energy.

Explain the difference between inelastic and perfectly inelastic collisions.

Two billiard balls of equal mass are traveling straight toward each other with the same speed. They meet head-on in an elastic collision. What is the total momentum of the system containing the two balls before the collision?

A 0.16 kg billiard ball moving to the right at 1.2 m/s has a head-on elastic collision with another ball of equal mass moving to the left at 0.85 m/s. The first ball moves to the left at 0.85 m/s after the collision. Find the velocity of the second ball after the collision, and verify your answer by calculating the total kinetic energy before and after the collision.

A 0.10 kg object makes an elastic head-on collision with a 0.15 kg stationary object. The final velocity of the 0.10 kg object after the collision is 0.045 m/s, and the final velocity of the 0.15 kg object after the collision is 0.16 m/s. What was the initial velocity of the 0.10 kg object?

A 90 kg halfback runs north and is tackled by a 120 kg opponent running south at 4 m/s. The collision is perfectly inelastic. Just after the tackle, both players move at a velocity of 2 m/s north. Calculate the velocity of the 90 kg player just before the tackle.

An 8 kg cart is released at the top of a 30o ramp. The cart rolls 4 m down the ramp and collides with an identical stationary cart at the bottom of the ramp. The two carts stick together and continue to roll horizontally.

a. Calculate the final velocity of the two carts after the collision.

b. Calculate the energy lost from kinetic energy during the collision.

c. What forms of energy did the lost kinetic energy turn into?