Answer:
392
Explanation:
According to the law of conservation of energy, energy cannot vanish,so the lost potential energy must be converted into another form of energy (in this case, Kinetic Energy).
(mass*g*height)-(mass*g*halfway height)=(2*9.8*40)-(2*9.8*20)
784-392=392
This makes sense because since the rock has fallen halfway, half of its potential energy has become kinetic energy. Once the rock reaches a height of 0 Meter, all of its potential energy will be kinetic energy.
