List three cases in which potential energy becomes
kinetic energy and three cases in which kinetic
energy becomes potential energy

1 Electrical Potential Energy, separating two charged plates will store energy as the plates want to return to their original position. 

2 Spring or Elastic can be stretched to store energy as it wants to return to rest 

3 Gravitational energy is stored by moving something (ball or pendulum are both examples of this) against a gravity gradient (lifting an object) that wants to fall back down.