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.
Vertical displacement = h = 5 m
Mass of the object = m = 40 kg
Acceleration due to gravity = g = 9.8 m/s
Gravitational potential energy is given by the expression,
W = mgh
∴ W = 40 × 9.8 × 5 = 1960 J.
At half-way down, the potential energy of the object will be 1960 / 2 = 980 J.
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Fig. 8.11
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Fig. 8.12
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