chapter 9

An artillery shell explodes in midair and breaks up into many fragments. Which of the following statements are true regarding conditions immediately before and immediately after the explosion: I. The total momentum of the fragments is equal to the original momentum of the shell. II. The total kinetic energy of the fragments is equal to the original kinetic energy of the shell. a. Statement I only b. Statement II only c. Both Statement I and Statement II d. Neither statement is true.

a. Statement I only

A stunt person jumps from the roof of a tall building, but no injury occurs because the person lands on a large, air-filled bag. Which one of the following best describes why no injury occurs? a. The bag increases the amount of time during which the momentum is changing and reduces the average force on the person. b. The bag decreases the amount of time during which the momentum is changing and reduces the average force on the person. c. The bag increases the amount of time the force acts on the person and reduces the change in momentum. d. The bag provides the necessary force to stop the person.

a. The bag increases the amount of time during which the momentum is changing and reduces the average force on the person.

A freight car moves along a frictionless level railroad track at constant speed. The freight car is open on the top. A large load of sand is suddenly dumped into the freight car. What happens to the speed of the freight car? a. The speed of the freight car decreases. b. The speed of the freight car increases. c. The speed of the freight car remains constant. d. The speed of the freight car cannot be determined from the information given.

a. The speed of the freight car decreases.

Which one of the following provides a basis to distinguish different types of collisions? a. conservation of kinetic energy b. conservation of linear momentum c. conservation of impulse d. conservation of mass

a. conservation of kinetic energy

A rubber ball and a lump of putty have equal mass. They are thrown with equal speed against a wall. The ball bounces back with nearly the same speed with which it hit. The putty sticks to the wall. Which objects experiences the lessor momentum change? a. the ball b. Both experience the same non-zero momentum change. c. Both experience zero momentum change. d. the putty

a. the ball

You are standing on a skateboard, initially at rest. A friend throws a very heavy ball towards you. You can either catch the object or deflect the object back towards your friend (such that it moves away from you with the same speed as it was originally thrown). What should you do in order to maximize your speed on the skateboard? a. Catch the ball. b. Deflect the ball. c. Your final speed on the skateboard will be the same regardless whether you catch the ball or deflect the ball. d. There is not enough information given to determine an answer.

b. Deflect the ball.

Jacques and George meet in the middle of a lake while paddling in their canoes. They come to a complete stop and talk for a while. When they are ready to leave, Jacques pushes George's canoe with a force to separate the two canoes. What is correct to say about the final momentum and kinetic energy of the system? a. The final momentum is in the direction of the force and the final kinetic energy is positive. b. The final momentum is zero kg∙m/s but the final kinetic energy is positive. c. The final momentum is in the direction of the force but the final kinetic energy is zero J. d. The final momentum is zero kg∙m/s and the final kinetic energy is zero J.

b. The final momentum is zero kg∙m/s but the final kinetic energy is positive.

An inelastic collision of two objects is characterized by the following. a. Total kinetic energy of the system is conserved. b. Total momentum of the system remains constant. c. Both A and B are true. d. Neither A nor B are true.

b. Total momentum of the system remains constant.

Two pucks on an air hockey table collide elastically. Complete the following statement: when such a collision occurs in two dimensions, the before and after velocities are best determined by a. using the fact that total kinetic energy is conserved. b. remembering the momentum is a vector quantity that is conserved in each direction. c. making use of the work-energy theorem. d. using the fact that momentum is conserved and that the initial speeds of the objects must equal the final speeds of the objects.

b. remembering the momentum is a vector quantity that is conserved in each direction.

A ping-pong ball moving east at a speed of 4 m/s, collides with a stationary bowling ball. The Ping-Pong ball bounces back to the west, and the bowling ball moves very slowly to the east. Which object experiences the greater magnitude impulse during the collision? a. It's impossible to tell since the velocities after the collision are unknown. b. the Ping-Pong ball c. Neither; both experienced the same magnitude impulse. d. the bowling ball

c. Neither; both experienced the same magnitude impulse.

In a lab environment, you are investigating the impulse of a force exerted on a brick when the brick's speed is reduced from 2.5 m/s to a complete stop. First, you allow the brick to slam into a secured piece of wood, bringing the brick to a sudden stop. Second, you allow the brick to plow into a large slab of gelatin so that the brick comes to a gradual halt. In which situation is there a greater impulse of the force on the brick? a. Not enough information is given to determine the answer. b. There is a greater impulse of the force on the brick from the gelatin. c. The impulse is the same in both situations. d. There is a greater impulse of the force on the brick from the wall.

c. The impulse is the same in both situations.

A collision between two objects is elastic. Which one of the following statements concerning this situation is true? a. The total momentum of the objects is zero kg*m/s after the collision. b. The vector sum of the velocities of the two objects is equal to zero m/s after the collision. c. The total kinetic energy of the objects is the same before and after the collision. d. The objects stick together and move as one after the collision.

c. The total kinetic energy of the objects is the same before and after the collision.

When a person steps forward out of a small boat onto a dock, the boat recoils backward in the water. Why does this occur? a. The momentum of the boat is greater than the momentum of the person. b. The energy of the person is greater than the energy of the boat. c. The total momentum of the system is conserved. d. The momentum of the person is greater than the momentum of the boat.

c. The total momentum of the system is conserved.

Complete the following statement: The change in momentum with respect to time for an object a. is always positive. b. is a scalar quantity that may be negative, zero, or positive. c. has a constant value if the force acting on the object is conservative. d. is equal in magnitude to the net force acting on the object, but opposite in direction.

c. has a constant value if the force acting on the object is conservative.

Complete the following statement: The center of mass is a. the region of an object where most of the mass is located. b. the point at the geometrical center of an object. c. the only point on an object at which the gravitational force acts. d. the point within an object that moves as if all of the object's mass were located there.

d. the point within an object that moves as if all of the object's mass were located there.