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

As the first cart is given a blow, it gains kinetic energy and moves forward. meanwhile, the spring stretches and kinetic energy gets converted into potential energy. This makes the spring pull on the second cart, again converting its spring potential energy into kinetic energy of the second cart. As the second cart moves forward, it makes the spring compress, making it gain potential energy. The spring in turn pushes the first cart forward, converting its spring potential energy into kinetic energy of the cart. This is why the system moves in a jerky manner.