Question

A ball hits a horizontal spring. As the spring is compressed, the ball comes to a stop. Then the spring pushes the ball back in the direction it came. Which one of the following describes the momentum of the system? *

The momentum of the system is larger after the collision with the spring.

The momentum of the system is smaller after the collision with the spring.

The momentum of the system is conserved before and after the collision with the spring, but not during the collision.

The momentum of the system is conserved before, during, and after the collision with the spring.

Answer 1

The correct answer is option (3) i.e. The momentum of the system is conserved before and after the collision ,but not during the collision .

Explanation :

• When the ball hits the spring , the spring gets compressed and at maximum compression the velocity of ball is zero.
• At this time the spring tip is also stationary , so total momentum is zero despite of some initial momentum .
• However , under the action of conservative force of string the ball regains the same velocity , thus momentum is conserved .

Hence  , the momentum of the system remains conserved before and after the collision of ball with spring but not conserved during the collision .

Answer 2

The law of momentum conservation can be stated as follows. For a collision occurring between object 1 and object 2 in an isolated system, the total momentum of the two objects before the collision is equal to the total momentum of the two objects after the collision.