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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 :

Gravitational mechanical energy is given by the expression,

\( W = mgh \)


h = Vertical displacement = 5 m, m = Mass of the item = 40 kg

g = Acceleration because of gravity = 9.8 m s-2

\( \therefore W = 40 × 5 × 9.8 = 1960 \ J \) .

At half-way down, the mechanical energy of the item are going to be \( \frac{1960}{2} \)

At this time, the item has an equal quantity of potential and K.E.

This can be due to law of conservation of energy. Hence, half-way down, the K.E. of the item can be 980 J.

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