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
