1. Halliday/Resnick/Walker Fundamentals of Physics 8th edition
Classroom Response System Questions
Chapter 9 Center of Mass and Linear Momentum
Reading Quiz Questions

2. 9.2.1. Complete the following statement: The center of mass is
a) the region of an object where the density has the largest value.
b) the region of an object where most of the mass is located.
c) the point within an object that moves as if all of the object’s mass where located there.
d) the point at the geometrical center of an object.
e) the only point on an object at which the gravitational force acts.

3. 9.2.1. Complete the following statement: The center of mass is
a) the region of an object where the density has the largest value.
b) the region of an object where most of the mass is located.
c) the point within an object that moves as if all of the object’s mass where located there.
d) the point at the geometrical center of an object.
e) the only point on an object at which the gravitational force acts.

4. 9.2.2. Which one of the following statements concerning the center of mass of an object is true?
a) 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.
b) The center of mass of a system of objects cannot change even if there are forces acting on the objects.
c) All of an object’s mass is located at its center of mass.
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 center of mass of an object must be located within the object.

5. 9.2.2. Which one of the following statements concerning the center of mass of an object is true?
a) 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.
b) The center of mass of a system of objects cannot change even if there are forces acting on the objects.
c) All of an object’s mass is located at its center of mass.
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 center of mass of an object must be located within the object.

6. Three objects are located in the x-y­ plane as shown in the figure. Determine the x coordinate of the center of mass for this system of three objects. Note the masses of the objects: mA = 6.0 kg, mB = 2.0 kg, and mC = 4.0 kg.
a) 5.6
b) 6.3
c) 7.6
d) 8.3
e) 8.9

7. Three objects are located in the x-y­ plane as shown in the figure. Determine the x coordinate of the center of mass for this system of three objects. Note the masses of the objects: mA = 6.0 kg, mB = 2.0 kg, and mC = 4.0 kg.
a) 5.6
b) 6.3
c) 7.6
d) 8.3
e) 8.9

8. Complete the following statement: the center of mass of a system of particles has a constant velocity if
a) the velocity of the center of mass is initially zero.
b) the particles are distributed symmetrically around the center of mass.
c) the forces exerted by the particles on each other sum to zero.
d) the center of mass is at the geometric center of the system.
e) the external forces acting on particles of the system sum to zero.

9. Complete the following statement: the center of mass of a system of particles has a constant velocity if
a) the velocity of the center of mass is initially zero.
b) the particles are distributed symmetrically around the center of mass.
c) the forces exerted by the particles on each other sum to zero.
d) the center of mass is at the geometric center of the system.
e) the external forces acting on particles of the system sum to zero.

10. 9.3.1. Complete the following statement: The change in momentum with respect to time for an object
a) is always positive.
b) is always equal to zero.
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.
e) is a scalar quantity that may be negative, zero, or positive.

11. 9.3.1. Complete the following statement: The change in momentum with respect to time for an object
a) is always positive.
b) is always equal to zero.
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.
e) is a scalar quantity that may be negative, zero, or positive.

12. Which one of the following statements concerning the momentum of a system when the net force acting on the system is equal to zero newtons is true?
a) The momentum of the system is increasing.
b) The momentum of the system is decreasing.
c) The momentum of the system is equal to zero kgm/s.
d) The momentum of the system has a constant value.
e) The momentum of the system has a negative value.

13. Which one of the following statements concerning the momentum of a system when the net force acting on the system is equal to zero newtons is true?
a) The momentum of the system is increasing.
b) The momentum of the system is decreasing.
c) The momentum of the system is equal to zero kgm/s.
d) The momentum of the system has a constant value.
e) The momentum of the system has a negative value.

14. Which one of the following statements concerning the momentum of a system when the net force acting on the system has a positive value is true?
a) The momentum of the system is increasing.
b) The momentum of the system is decreasing.
c) The momentum of the system is equal to zero kgm/s.
d) The momentum of the system has a constant value.
e) The momentum of the system has a negative value.

15. Which one of the following statements concerning the momentum of a system when the net force acting on the system has a positive value is true?
a) The momentum of the system is increasing.
b) The momentum of the system is decreasing.
c) The momentum of the system is equal to zero kgm/s.
d) The momentum of the system has a constant value.
e) The momentum of the system has a negative value.

16. 9.4.1. Which one of the following statements is true concerning momentum?
a) Momentum is a force.
b) Momentum is a velocity.
c) Momentum is a scalar quantity.
d) The momentum of an object is always positive.
e) Momentum is measured in kg  m/s.

17. 9.4.1. Which one of the following statements is true concerning momentum?
a) Momentum is a force.
b) Momentum is a velocity.
c) Momentum is a scalar quantity.
d) The momentum of an object is always positive.
e) Momentum is measured in kg  m/s.

18. 9.4.2. Momentum may be expressed using which of the following units?
a) N / s
b) kg / m
c) kg  m/s
d) kg / (m  s)
e) N  kg / s

19. 9.4.2. Momentum may be expressed using which of the following units?
a) N / s
b) kg / m
c) kg  m/s
d) kg / (m  s)
e) N  kg / s

20. 9.4.3. The momentum of an object is not dependent on which one of the following quantities?
a) acceleration
b) inertia
c) mass
d) speed
e) velocity

21. 9.4.3. The momentum of an object is not dependent on which one of the following quantities?
a) acceleration
b) inertia
c) mass
d) speed
e) velocity

22. As the name implies, the linear momentum-impulse theorem provides a relationship between impulse and momentum. Which one of the following statements correctly describes that relationship?
a) An impulse is equal to the work done on an object when a net force acts on an object and it has a displacement.
b) An impulse is equal to the change in an object’s momentum that occurs when a
net force acts on it.
c) An impulse is equal to one-half of the object’s momentum squared.
d) An impulse is equal to the product of the net force acting on the object and its momentum.
e) An impulse is equal to the object’s momentum divided by the product of the net force and the time interval during which the force acts.

23. As the name implies, the linear momentum-impulse theorem provides a relationship between impulse and momentum. Which one of the following statements correctly describes that relationship?
a) An impulse is equal to the work done on an object when a net force acts on an object and it has a displacement.
b) An impulse is equal to the change in an object’s momentum that occurs when a
net force acts on it.
c) An impulse is equal to one-half of the object’s momentum squared.
d) An impulse is equal to the product of the net force acting on the object and its momentum.
e) An impulse is equal to the object’s momentum divided by the product of the net force and the time interval during which the force acts.

24. 9.6.2. Which of the following units are used for an impulse?
a) kg  m/s
b) kg / m
c) N / s
d) kg / (m  s)
e) N  kg / s

25. 9.6.2. Which of the following units are used for an impulse?
a) kg  m/s
b) kg / m
c) N / s
d) kg / (m  s)
e) N  kg / s

26. Which one of the following quantities is equal to the change in momentum of an object during a collision?
a) impulse
b) net force
c) work
d) change in kinetic energy
e) maximum force

27. Which one of the following quantities is equal to the change in momentum of an object during a collision?
a) impulse
b) net force
c) work
d) change in kinetic energy
e) maximum force

28. 9.7.1. In which one of the following situations is linear momentum not conserved?
a) A golf ball is struck by a putter.
b) A bowling ball collides with ten pins.
c) A tree limb is struck by lightning and falls to the ground.
d) A bomb suspended by a string explodes into one hundred fragments.
e) An astronaut floating in space throws a hammer away and subsequently moves in the opposite direction.

29. 9.7.1. In which one of the following situations is linear momentum not conserved?
a) A golf ball is struck by a putter.
b) A bowling ball collides with ten pins.
c) A tree limb is struck by lightning and falls to the ground.
d) A bomb suspended by a string explodes into one hundred fragments.
e) An astronaut floating in space throws a hammer away and subsequently moves in the opposite direction.

30. A rocket is propelled forward as very high speed gases are ejected out of its back. Which one of the following is the best explanation as to why the rocket is propelled forward?
a) The rocket is propelled forward due to the conservation of energy.
b) The rocket is propelled forward due to the conservation of momentum.
c) Because the gases are pushing against the air, the air propels the rocket forward.
d) The rocket is propelled forward because both energy and momentum must be conserved.
e) The high speed gases push on the rocket as they are ejected and propel it forward.

31. A rocket is propelled forward as very high speed gases are ejected out of its back. Which one of the following is the best explanation as to why the rocket is propelled forward?
a) The rocket is propelled forward due to the conservation of energy.
b) The rocket is propelled forward due to the conservation of momentum.
c) Because the gases are pushing against the air, the air propels the rocket forward.
d) The rocket is propelled forward because both energy and momentum must be conserved.
e) The high speed gases push on the rocket as they are ejected and propel it forward.

32. During a certain process, the linear momentum of a system is conserved. Which one of the following statements concerning this system is correct?
a) The vector sum of the momentum of the objects that make up the system is equal to zero kg  m/s.
b) The vector sum of any internal forces within the system results in an acceleration of one or more objects within the system.
c) The principle of the conservation of mechanical energy automatically applies to the system.
d) The vector sum of the average external forces acting on the system is equal to zero newtons.
e) No internal or external forces are acting on the objects within the system.

33. During a certain process, the linear momentum of a system is conserved. Which one of the following statements concerning this system is correct?
a) The vector sum of the momentum of the objects that make up the system is equal to zero kg  m/s.
b) The vector sum of any internal forces within the system results in an acceleration of one or more objects within the system.
c) The principle of the conservation of mechanical energy automatically applies to the system.
d) The vector sum of the average external forces acting on the system is equal to zero newtons.
e) No internal or external forces are acting on the objects within the system.

34. 9. 7. 4. A rifle of mass M is initially at rest
A rifle of mass M is initially at rest. A bullet of mass m is fired from the rifle with a velocity v relative to the ground. Which one of the following expressions gives the velocity of the rifle relative to the ground after the bullet is fired.
a) mv
b) mv
c) Mv/m
d) mv/M
e) mv/M

35. 9. 7. 4. A rifle of mass M is initially at rest
A rifle of mass M is initially at rest. A bullet of mass m is fired from the rifle with a velocity v relative to the ground. Which one of the following expressions gives the velocity of the rifle relative to the ground after the bullet is fired.
a) mv
b) mv
c) Mv/m
d) mv/M
e) mv/M

36. 9. 8. 1. A collision between two objects is elastic
A collision between two objects is elastic. Which one of the following statements concerning this situation is true?
a) The total kinetic energy of the objects is the same before and after the collision.
b) The total momentum of the objects is zero kgm/s after the collision.
c) The objects stick together and move as one object after the collision.
d) The kinetic energy of the objects is zero joules after the collision.
e) The vector sum of the velocities of the two objects is equal to zero m/s after the collision.

37. 9. 8. 1. A collision between two objects is elastic
A collision between two objects is elastic. Which one of the following statements concerning this situation is true?
a) The total kinetic energy of the objects is the same before and after the collision.
b) The total momentum of the objects is zero kgm/s after the collision.
c) The objects stick together and move as one object after the collision.
d) The kinetic energy of the objects is zero joules after the collision.
e) The vector sum of the velocities of the two objects is equal to zero m/s after the collision.

38. 9.8.2. Which one of the following provides a basis to distinguish different types of collisions?
a) conservation of linear momentum
b) conservation of mechanical energy
c) conservation of kinetic energy
d) conservation of impulse
e) conservation of mass

39. 9.8.2. Which one of the following provides a basis to distinguish different types of collisions?
a) conservation of linear momentum
b) conservation of mechanical energy
c) conservation of kinetic energy
d) conservation of impulse
e) conservation of mass

40. 9. 8. 3. A collision between two objects is inelastic
A collision between two objects is inelastic. Which one of the following statements concerning this situation is true?
a) The vector sum of the velocities of the two objects is equal to zero m/s after the collision.
b) The total momentum of the objects after the collision is less than it was before the collision.
c) The objects bounce away from each other after the collision.
d) The kinetic energy of the objects is zero joules after the collision.
e) The total kinetic energy of the objects after the collision is less than it was before the collision.

41. 9. 8. 3. A collision between two objects is inelastic
A collision between two objects is inelastic. Which one of the following statements concerning this situation is true?
a) The vector sum of the velocities of the two objects is equal to zero m/s after the collision.
b) The total momentum of the objects after the collision is less than it was before the collision.
c) The objects bounce away from each other after the collision.
d) The kinetic energy of the objects is zero joules after the collision.
e) The total kinetic energy of the objects after the collision is less than it was before the collision.

42. A boy of mass m runs with a speed v and jumps onto a sled on an icy pond. The sled was at rest before the boy jumped onto it. After the jump, the sled and boy move at a speed v/2. What is the mass of the sled?
a) m/2
b) m
c) 2m
d) 3m
e) 4m

43. A boy of mass m runs with a speed v and jumps onto a sled on an icy pond. The sled was at rest before the boy jumped onto it. After the jump, the sled and boy move at a speed v/2. What is the mass of the sled?
a) m/2
b) m
c) 2m
d) 3m
e) 4m

44. 9. 8. 5. Two objects are involved in an elastic collision
Two objects are involved in an elastic collision. Which one of the following statements concerning this situation is false?
a) The total momentum is conserved.
b) The magnitude of the force exerted by each object on the other object is equal.
c) The kinetic energy of each object is the same before and after the collision.
d) The total kinetic energy before the collision is equal to the total kinetic energy after the collision.
e) The total kinetic energy is conserved.

45. 9. 8. 5. Two objects are involved in an elastic collision
Two objects are involved in an elastic collision. Which one of the following statements concerning this situation is false?
a) The total momentum is conserved.
b) The magnitude of the force exerted by each object on the other object is equal.
c) The kinetic energy of each object is the same before and after the collision.
d) The total kinetic energy before the collision is equal to the total kinetic energy after the collision.
e) The total kinetic energy is conserved.

46. During a maneuver in space, a space craft separates into two pieces, each of mass m. Before the separation, the spacecraft was moving with a speed v. If one of the pieces is at rest after the separation, which one of the following statements concerning this maneuver is true?
a) This maneuver conserves kinetic energy.
b) The maneuver does not conserve total energy.
c) This maneuver does not conserve momentum.
d) If one piece is at rest, the other is moving with a speed 2v.
e) One piece cannot be at rest. The must both be moving with a speed v/2.

47. During a maneuver in space, a space craft separates into two pieces, each of mass m. Before the separation, the spacecraft was moving with a speed v. If one of the pieces is at rest after the separation, which one of the following statements concerning this maneuver is true?
a) This maneuver conserves kinetic energy.
b) The maneuver does not conserve total energy.
c) This maneuver does not conserve momentum.
d) If one piece is at rest, the other is moving with a speed 2v.
e) One piece cannot be at rest. The must both be moving with a speed v/2.

48. Which one of the following quantities is conserved during an elastic collision, but not conserved during an inelastic collision?
a) momentum
b) kinetic energy
c) total energy
d) impulse
e) net force

49. Which one of the following quantities is conserved during an elastic collision, but not conserved during an inelastic collision?
a) momentum
b) kinetic energy
c) total energy
d) impulse
e) net force

50. 9. 8. 8. A ball strikes a spring mounted on a wall
A ball strikes a spring mounted on a wall. As the spring is compressed the ball comes to a stop and then rebounds back in the direction it came. Which one of the following statements correctly describes the momentum of the system?
a) The momentum of the system is larger after the collision with the spring.
b) The momentum of the system is smaller after the collision with the spring.
c) The momentum of the system is conserved before and after the collision with the spring, but not during the collision.
d) The momentum of the system is conserved before, during, and after the collision with the spring.

51. 9. 8. 8. A ball strikes a spring mounted on a wall
A ball strikes a spring mounted on a wall. As the spring is compressed the ball comes to a stop and then rebounds back in the direction it came. Which one of the following statements correctly describes the momentum of the system?
a) The momentum of the system is larger after the collision with the spring.
b) The momentum of the system is smaller after the collision with the spring.
c) The momentum of the system is conserved before and after the collision with the spring, but not during the collision.
d) The momentum of the system is conserved before, during, and after the collision with the spring.

52. Bird A, with a mass of 2.2 kg, is stationary while Bird B, with a mass of 1.7 kg, is moving due north from Bird A at 3 m/s. What is the velocity of the center of mass for this system of two birds?
a) 1.4 m/s, due north
b) m/s, due north
c) 1.7 m/s, due north
d) m/s, due south
e) 1.4 m/s, due south

53. Bird A, with a mass of 2.2 kg, is stationary while Bird B, with a mass of 1.7 kg, is moving due north from Bird A at 3 m/s. What is the velocity of the center of mass for this system of two birds?
a) 1.4 m/s, due north
b) m/s, due north
c) 1.7 m/s, due north
d) m/s, due south
e) 1.4 m/s, due south

54. Car A with a mass 2m is traveling due west at 20 m/s when it collides with car B traveling due west at 30 m/s. The mass of car B is m. If the collision occurred on an icy road, so that the surface is essentially frictionless, what is the final velocity of the cars, which became locked together during the collision?
a) The cars are stationary.
b) 10 m/s, due east
c) 10 m/s, due west
d) 20 m/s, due west
e) None of the above answers is correct.

55. Car A with a mass 2m is traveling due west at 20 m/s when it collides with car B traveling due west at 30 m/s. The mass of car B is m. If the collision occurred on an icy road, so that the surface is essentially frictionless, what is the final velocity of the cars, which became locked together during the collision?
a) The cars are stationary.
b) 10 m/s, due east
c) 10 m/s, due west
d) 20 m/s, due west
e) None of the above answers is correct.

56. 9. 11. 1. Two pucks on an air hockey table collide elastically
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 momentum is conserved and that the initial speeds of the objects must equal the final speeds of the objects.
b) remembering that momentum is a vector quantity that is conserved in each direction.
c) applying Newton’s second law of motion and setting the net force equal to zero newtons.
d) making use of the work-energy theorem.
e) using the fact that the total energy is conserved.

57. 9. 11. 1. Two pucks on an air hockey table collide elastically
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 momentum is conserved and that the initial speeds of the objects must equal the final speeds of the objects.
b) remembering that momentum is a vector quantity that is conserved in each direction.
c) applying Newton’s second law of motion and setting the net force equal to zero newtons.
d) making use of the work-energy theorem.
e) using the fact that the total energy is conserved.

58. A rocket of mass M is launched vertically upward from the surface of the Earth. The rocket accelerates upward with a constant acceleration a. Which one of the following expressions gives the rate at which fuel is being consumed by the rocket?
a) R = 2Mvrel2/a
b) R = Ma
c) R = vrel2/2Ma d) e)

59. A rocket of mass M is launched vertically upward from the surface of the Earth. The rocket accelerates upward with a constant acceleration a. Which one of the following expressions gives the rate at which fuel is being consumed by the rocket?
a) R = 2Mvrel2/a
b) R = Ma
c) R = vrel2/2Ma d) e)