Question

An object of mass 40 kg is raised to a height of 5 m above the ground. What is its potential energy? If the object is allowed to fall, find its kinetic energy when it is half-way down.

Answer 1

We know that, potential energy = mgh 

Where, m = 40 kg 

g = 9.8 m/s² 

h = 5 m 

So, the potential energy = 40 × 9.8 × 5 J = 1960 J 

According to law of conservation of energy, the total mechanical energy (Kinetic and potential energy) of an object remains constant. 

Therefore, when the object is half-way down, its potential energy become half the original energy and remaining half converted into kinetic energy. 

Hence, the kinetic energy = ½ (1960) J = 980 J