Newton's third law and conservation of linear momentum — NEET & JEE Questions

Question 1 · difficulty L1 · recall

Newton's third law states that if body A exerts a force on body B, then body B exerts on A

• A. an equal and opposite force
• B. a smaller force in the same direction
• C. no force
• D. a force only if B is moving

Question 2 · difficulty L2 · understanding

Action and reaction forces do not cancel each other on a single body because they

• A. act on different bodies
• B. have different magnitudes
• C. always act at different times
• D. are perpendicular

Question 3 · difficulty L2 · understanding

Conservation of linear momentum for a system follows when the net external force on the system is

• A. zero
• B. maximum
• C. equal to its weight
• D. always internal

Question 4 · difficulty L2 · understanding

When a gun fires a bullet, the gun recoils because

• A. the gun and bullet exert equal and opposite forces on each other
• B. the bullet exerts a force but the gun does not
• C. momentum is created from nothing
• D. gravity pushes the gun backward

Question 5 · difficulty L3 · application

A $2\,\text{kg}$ body moving at $3\,\text{m s}^{-1}$ has what linear momentum?

• A. 1.5 kg m/s
• B. 5 kg m/s
• C. 6 kg m/s
• D. 9 kg m/s

Question 6 · difficulty L3 · application

A $4\,\text{kg}$ object initially at rest explodes into two fragments of masses 1 kg and 3 kg. If the 1 kg fragment moves east at 6 m/s, what is the velocity of the 3 kg fragment?

• A. 2 m/s east
• B. 2 m/s west
• C. 6 m/s west
• D. 18 m/s west

Question 7 · difficulty L3 · application

A 60 kg person jumps from a stationary 120 kg boat at 3 m/s relative to the shore. Neglecting external horizontal forces, what is the boat's velocity?

• A. 0.5 m/s opposite
• B. 1.5 m/s opposite
• C. 3 m/s opposite
• D. 6 m/s opposite

Question 8 · difficulty L3 · application

A force of 10 N acts on an object for 0.20 s. What change in momentum does it produce?

• A. 0.5 kg m/s
• B. 2 kg m/s
• C. 10 kg m/s
• D. 50 kg m/s

Question 9 · difficulty L4 · application

Two skaters initially at rest push off from each other. One has mass 50 kg and moves at 4 m/s east. The other has mass 80 kg. What is the second skater's velocity?

• A. 2.5 m/s west
• B. 4 m/s west
• C. 6.4 m/s west
• D. 2.5 m/s east

Question 10 · difficulty L4 · application

A truck collides with a small car. During the collision, which statement about the interaction forces is correct?

• A. The truck exerts a larger force on the car
• B. The car exerts a larger force on the truck
• C. They exert equal-magnitude opposite forces on each other
• D. The forces are equal only if the vehicles have equal masses