Question

Two identical carts on a frictionless air track are attached by a spring. One is suddenly struck a blow that sends it moving away from the other cart. The motion of the carts is seen to be very jerky-first one cart moves, then stops as the other cart moves and stops in its turn. Explain the motion in a qualitative way.

Answer 1

This is due to the compression and expansion of the spring.

When the first car moves away the spring connecting the two cars stretches as it stretches it develops a spring force opposite to the expansion or acting inwards to bring back the spring in shape. After maximum elongation the side which is connected to first car comes to rest and the other end pulls the second car toward the first. Then spring begins to compress. And when it is being compressed it again develops a spring force trying to push the cars away. Due to the momentum of second car it doesn't gets pushed but begins to slow and the first car which is at rest begins to move away.