Concepts chapter 7

A rock is dropped from a high tower and falls freely under the influence of gravity. Which one of the following statements concerning the rock as it falls is true? Neglect the effects of air resistance. A) The rock will gain an equal amount of momentum during each second. B) The rock will gain an equal amount of kinetic energy during each second. C) The rock will gain an equal amount of speed for each meter through which it falls. D) The rock will gain an equal amount of momentum for each meter through which it falls. E) The amount of momentum the rock gains will be proportional to the amount of potential energy that it loses.

A

A tennis ball has a velocity of 12 m/s downward just before it strikes the ground and bounces up with a velocity of 12 m/s upward. Which statement is true concerning this situation? A) The momentum of the ball and the momentum of the earth both change. B) Neither the momentum of the ball nor the momentum of the earth changes. C) The momentum of the ball is changed; and the momentum of the earth is not changed. D) The momentum of the ball is unchanged; and the momentum of the earth is changed. E) Both the momentum and the kinetic energy of the ball change because of the collision.

A

Complete the following statement: Different types of collisions between interacting bodies are categorized on the basis of A) kinetic energy conservation. B) mechanical energy conservation. C) linear momentum conservation. D) the magnitude of the forces involved. E) the temporal duration of the collision.

A

While in Earth's orbit, an 80-kg astronaut carrying a 20-kg tool kit is initially drifting toward a stationary (relative to her) space shuttle at a speed of 2 m/s. If she throws the tool kit toward the shuttle with a speed of 6 m/s as seen from the shuttle, her final speed is A) 1 m/s toward the shuttle. B) 1 m/s away from the shuttle. C) 2 m/s toward the shuttle. D) 4 m/s toward the shuttle. E) 6 m/s away from the shuttle.

A

A sled of mass m is coasting on the icy surface of a frozen river. While it is passing under a bridge, a package of equal mass m is dropped straight down and lands on the sled (without causing any damage). The sled plus the added load then continue along the original line of motion. How does the kinetic energy of the (sled + load) compare with the original kinetic energy of the sled? A) It is 1/4 the original kinetic energy of the sled. B) It is 1/2 the original kinetic energy of the sled. C) It is 3/4 the original kinetic energy of the sled. D) It is the same as the original kinetic energy of the sled. E) It is twice the original kinetic energy of the sled.

B

Two objects constitute an isolated system. In an elastic collision between the two objects, which one of the following statements is a false statement? A) The total kinetic energy is conserved. B) The kinetic energy of each object is the same before and after the collision. C) The total momentum is conserved. D) The magnitude of the force exerted by each object on the other object is equal. E) The total kinetic energy before the collision is equal to the total kinetic energy after the collision.

B

An object of mass 3m, initially at rest, explodes breaking into two fragments of mass m and 2m, respectively. Which one of the following statements concerning the fragments after the explosion is true? A) They will fly off at right angles. B) They will fly off in the same direction. C) The smaller fragment will have twice the speed of the larger fragment. D) The larger fragment will have twice the speed of the smaller fragment. E) The smaller fragment will have four times the speed of the larger fragment.

C

A stationary bomb explodes in space breaking into a number of small fragments. At the location of the explosion, the net force due to gravity is zero newtons. Which one of the following statements concerning this event is true? A) Kinetic energy is conserved in this process. B) All of the fragments must have equal kinetic energies. C) The sum of the kinetic energies of the fragments must be zero. D) The vector sum of the linear momenta of the fragments must be zero. E) The mass of any one fragment must be equal to the mass of any other fragment.

D

Complete the following statement: Momentum will be conserved in a two-body collision only if A) both bodies come to rest. B) the collision is perfectly elastic. C) the kinetic energy of the system is conserved. D) the net external force acting on the two-body system is zero. E) the internal forces of the two body system cancel in action-reaction pairs.

D

Which one of the following is characteristic of an inelastic collision? A) Total mass is not conserved. B) Total energy is not conserved. C) Linear momentum is not conserved. D) Kinetic energy is not conserved. E) The change in momentum is less than the total impulse.

D

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 provides the necessary force to stop the person. B) The bag reduces the impulse to 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 decreases the amount of time during which the momentum is changing and reduces the average force on the person. E) The bag increases the amount of time during which the momentum is changing and reduces the average force on the person.

E

Complete the following statement: A collision is elastic if A) the final velocities are zero. B) the objects stick together. C) the final kinetic energy is zero. D) the final momentum is zero. E) the total kinetic energy is conserved.

E

In which one of the following situations is linear momentum not conserved? A) A bomb suspended by a string explodes into one hundred fragments. B) A bowling ball collides with a set of ten pins. C) A golf ball is struck by a club. D) An astronaut floating in space throws a hammer away and subsequently moves in the opposite direction. E) A tree limb is struck by lightning and falls to the ground.

E

Two objects of equal mass traveling toward each other with equal speeds undergo a head on collision. Which one of the following statements concerning their velocities after the collision is necessarily true? A) They will exchange velocities. B) Their velocities will be reduced. C) Their velocities will be unchanged. D) Their velocities will be zero. E) Their velocities may be zero.

E

Which one of the following statements concerning center of mass is true? A) All of an object's mass is located at its center of mass. B) The center of mass of an object must be located within the object. C) The center of mass of a system of objects cannot change even if there are forces acting on the objects. D) The velocity of the center of mass of a system of objects is greatly affected by a collision of objects within the system. E) The velocity of the center of mass of a system of objects is constant when the sum of the external forces acting on the system is zero.

E

Which one of the following statements concerning momentum is true? A) Momentum is a force. B) Momentum is a scalar quantity. C) The SI unit of momentum is kg ⋅ m2/s. D) The momentum of an object is always positive. E) Momentum and impulse are measured in the same units.

E