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08/01/2021 4:36 pm
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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.
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08/01/2021 4:43 pm
Potential energy of the object = m x g x h
= 40 kg x 10 ms-2 x 5 m
= 40 x 10 x 5 kg m s-2 = 2000 J
Let v be the velocity of the object at half the height i.e., after travelling 2.5 m.
Then v2 - u2 = 2as
v2 - 02 = 2 x 10 ms-2 x 2.5 m = 50 m2s-2
So, v2 = 50 m2s-2
Then,
Kinetic energy = \(\frac{1}{2}mv^2 \) = \(\frac{1}{2}\times 40kg \times 50 m^2s^{-2}\)
= 1000 J (∵ 1 J = 1 kg m2s-2)