30 MCQ based on conservation of momentum
1. What is the law of conservation of momentum?
A. Momentum is always increasing
B. Momentum is always decreasing
C. The total momentum of an isolated system remains constant
D. Momentum depends on the frame of reference
Explanation: The correct answer is C. According to the law of conservation of momentum, in an isolated system, the total momentum remains constant.
2. If no external forces act on a system, what can be said about the total momentum of the system?
A. It decreases
B. It increases
C. It remains constant
D. It depends on the masses involved
Explanation: The correct answer is C. In the absence of external forces, the total momentum of a system remains constant.
3. Two objects collide and bounce off each other. What can be said about the total momentum before and after the collision?
A. Before > After
B. Before < After
C. Before = After
D. Cannot be determined
Explanation: The correct answer is C. In the absence of external forces, the total momentum before a collision is equal to the total momentum after the collision.
4. Which of the following is an example of an isolated system for the conservation of momentum?
A. A moving car
B. A rolling ball on a table
C. A rocket in space with no external forces
D. A person jumping on a trampoline
Explanation: The correct answer is C. An isolated system for the conservation of momentum is one where no external forces act on it, such as a rocket in space.
5. If an object has zero momentum, what can be said about its motion?
A. It is stationary
B. It is moving with constant velocity
C. It is accelerating
D. It is experiencing a force
Explanation: The correct answer is A. If an object has zero momentum, it is stationary.
6. What is the mathematical expression for momentum?
A. Momentum = Force × Time
B. Momentum = Mass × Velocity
C. Momentum = Distance ÷ Time
D. Momentum = Acceleration × Mass
Explanation: The correct answer is B. The momentum of an object is given by the product of its mass and velocity, i.e., Momentum = Mass × Velocity.
7. In a closed system, if one object experiences an increase in momentum, what must happen to the momentum of another object in the system?
A. It must decrease
B. It must increase
C. It remains constant
D. It depends on the masses involved
Explanation: The correct answer is A. In a closed system, if one object experiences an increase in momentum, another object must experience a decrease in momentum to conserve the total momentum of the system.
8. Which of the following scenarios violates the conservation of momentum?
A. Two ice skaters pushing off each other and moving in opposite directions
B. A car colliding with a stationary wall and coming to rest
C. Two billiard balls colliding on a frictionless table
D. A rocket propelling itself forward in space
Explanation: The correct answer is B. In the scenario where a car collides with a stationary wall and comes to rest, external forces (from the wall) are involved, violating the conservation of momentum.
9. If a rocket is moving in space and expels gas backward, what happens to the rocket's momentum?
A. It increases
B. It decreases
C. It remains constant
D. It depends on the mass of the gas expelled
Explanation: The correct answer is C. The rocket's momentum remains constant because the expelled gas carries away momentum in the opposite direction.
10. What is the momentum of a 500 kg car traveling at a velocity of 20 m/s?
A. 10,000 kg·m/s
B. 5,000 kg·m/s
C. 25,000 kg·m/s
D. 1,000 kg·m/s
Explanation: The correct answer is B. Momentum = Mass × Velocity, so Momentum = 500 kg × 20 m/s = 10,000 kg·m/s.
11. When two objects of equal mass collide and stick together, what happens to their combined momentum compared to their individual momenta before the collision?
A. It increases
B. It decreases
C. It remains constant
D. It depends on the velocities before the collision
Explanation: The correct answer is C. When two objects of equal mass stick together after a collision, their combined momentum remains constant.
12. Which of the following statements best describes an elastic collision?
A. Kinetic energy is conserved
B. Momentum is not conserved
C. Total energy is constant
D. Objects stick together after the collision
Explanation: The correct answer is A. In an elastic collision, kinetic energy is conserved.
13. A ball bounces off a wall. What is the change in its momentum during the collision?
A. Zero
B. Positive
C. Negative
D. Depends on the mass of the ball
Explanation: The correct answer is C. The direction of the ball's velocity changes after bouncing off the wall, resulting in a change in momentum.
14. If the mass of an object is doubled, and its velocity is halved, how does its momentum change?
A. It is halved
B. It is doubled
C. It remains the same
D. It depends on the initial momentum
Explanation: The correct answer is A. Momentum is directly proportional to both mass and velocity. If mass is doubled and velocity is halved, the overall momentum is halved.
15. Which of the following is a vector quantity related to momentum?
A. Mass
B. Speed
C. Velocity
D. Kinetic energy
Explanation: The correct answer is C. Momentum is a vector quantity, and its direction is the same as the direction of the velocity.
16. In an isolated system, two objects with masses m1 and m2 move with velocities v1 and v2, respectively, before a collision. What is the total momentum of the system before the collision?
A. m1v1 + m2v2
B. m1v1 - m2v2
C. m1v1 × m2v2
D. m1v1 ÷ m2v2
Explanation: The correct answer is A. The total momentum of an isolated system before a collision is the sum of the individual momenta, which is m1v1 + m2v2.
17. What is the impulse experienced by an object if the force acting on it is doubled for the same amount of time?
A. It is halved
B. It is doubled
C. It remains the same
D. It depends on the initial impulse
Explanation: The correct answer is B. Impulse is the product of force and time, so if the force is doubled for the same amount of time, the impulse is doubled.
18. If the time of impact during a collision is increased, what happens to the force experienced by the objects involved?
A. It increases
B. It decreases
C. It remains the same
D. It depends on the masses of the objects
Explanation: The correct answer is B. Impulse is the product of force and time. If time is increased and impulse remains constant, the force experienced decreases.
19. Which of the following statements is correct regarding the conservation of momentum in a collision?
A. Momentum is conserved only in elastic collisions
B. Momentum is conserved only in inelastic collisions
C. Momentum is always conserved in all collisions
D. Momentum is conserved only if the objects stick together after a collision
Explanation: The correct answer is C. Momentum is always conserved in all collisions, regardless of whether they are elastic or inelastic.
20. A 1,000 kg car moving at 10 m/s collides with a stationary 500 kg car. After the collision, the two cars stick together. What is their final velocity?
A. 2 m/s
B. 4 m/s
C. 6 m/s
D. 8 m/s
Explanation: The correct answer is B. To find the final velocity, use the principle of conservation of momentum: (m1v1 + m2v2) = (m1 + m2)vf. Solving for vf gives (1000 kg × 10 m/s + 500 kg × 0 m/s) / (1000 kg + 500 kg) = 4 m/s.
21. Which of the following scenarios is an example of an inelastic collision?
A. Two billiard balls colliding and bouncing off each other
B. A rocket propelling itself forward in space
C. A car colliding with a stationary wall and sticking to it
D. Two ice skaters pushing off each other on frictionless ice
Explanation: The correct answer is C. In an inelastic collision, objects stick together after the collision, as seen in the scenario of a car colliding with a stationary wall and sticking to it.
22. What is the change in momentum if a force of 50 N is applied to an object for 2 seconds?
A. 25 kg·m/s
B. 50 kg·m/s
C. 100 kg·m/s
D. 200 kg·m/s
Explanation: The correct answer is C. Impulse, which is the change in momentum, is given by the product of force and time: Impulse = Force × Time = 50 N × 2 s = 100 kg·m/s.
23. A 200 g baseball is thrown with a velocity of 20 m/s. What is its momentum?
A. 2 kg·m/s
B. 4 kg·m/s
C. 6 kg·m/s
D. 8 kg·m/s
Explanation: The correct answer is C. Momentum = Mass × Velocity, so Momentum = 0.2 kg × 20 m/s = 4 kg·m/s.
24. In a closed system, if the net external force acting on the system is zero, what can be said about the total momentum of the system?
A. It increases
B. It decreases
C. It remains constant
D. It depends on the masses involved
Explanation: The correct answer is C. In the absence of a net external force, the total momentum of a closed system remains constant.
25. Which of the following equations represents the law of conservation of momentum for a two-object system before and after a collision?
A. m1v1 + m2v2 = m1v1' + m2v2'
B. m1v1 - m2v2 = m1v1' - m2v2'
C. m1v1 × m2v2 = m1v1' × m2v2'
D. m1v1 ÷ m2v2 = m1v1' ÷ m2v2'
Explanation: The correct answer is A. The law of conservation of momentum states that the total momentum before a collision is equal to the total momentum after the collision, so m1v1 + m2v2 = m1v1' + m2v2'.
26. Which of the following factors affects the amount of force experienced during a collision?
A. Mass
B. Velocity
C. Time of impact
D. All of the above
Explanation: The correct answer is D. The amount of force experienced during a collision is influenced by the mass, velocity, and time of impact.
27. Why does a rocket move forward in space when gases are expelled backward?
A. Conservation of energy
B. Conservation of momentum
C. Conservation of mass
D. Conservation of force
Explanation: The correct answer is B. According to the law of conservation of momentum, the rocket moves forward because the expelled gases carry momentum in the opposite direction.
28. A 300 kg car collides with a 500 kg car. If the 300 kg car was initially traveling at 15 m/s and comes to rest after the collision, what is the final velocity of the 500 kg car?
A. 3 m/s
B. 5 m/s
C. 7 m/s
D. 10 m/s
Explanation: The correct answer is D. Using the principle of conservation of momentum: m1v1 + m2v2 = m1v1' + m2v2'. Solving for v2' gives (300 kg × 15 m/s + 500 kg × 0 m/s) / 500 kg = 10 m/s.
29. If the momentum of an object is doubled, what can be said about its kinetic energy?
A. It is halved
B. It is doubled
C. It remains the same
D. It depends on the mass of the object
Explanation: The correct answer is B. Kinetic energy is directly proportional to the square of the velocity. If momentum is doubled, velocity is doubled
30. Two identical railway cars, initially at rest, are on a straight track. Car A explodes into two fragments, one of which moves forward with twice the speed of the other. If there are no external forces, what can be said about the mass of the two fragments and the direction in which they move?
- A. The fragments have equal masses, and both move in the same direction.
- B. The fragments have equal masses, and they move in opposite directions.
- C. The fragment with higher speed has less mass, and they move in opposite directions.
- D. The fragment with higher speed has more mass, and they move in the same direction.
Explanation: The correct answer is C. According to the conservation of momentum, the total momentum before the explosion is zero (as the system is initially at rest). After the explosion, the fragments move in opposite directions, and the one with higher speed must have less mass to conserve momentum.
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