Question

When an apple falls from a tree what happens to its gravitational potential energy just as it reaches the ground? After it strikes the ground?

Answer 1

• Let us imagine an apple of mass ‘m’ falls from a height h. 
• Before starting to fall down, its velocity is zero. Hence its energy is purely potential. 
• When it falls down, its gravitational potential energy gradually converts into kinetic energy, but the entire energy in the system remains same. 
• When it strikes the ground, its energy is fully kinetic, till its velocity becomes zero.