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The height to which the body reaches after 2 seconds
S = ut + 1/2a t^2
= 15*2 - (1/2 * 10 * 4)
= 30 - 20
= 10 m
Potential energy gained by body = mgh = 1.5 * 10 * 10 = 150 J
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I have a doubt. In the first case we are taking a=g as negative.
But in the second case we take it as positive. Why??
We are not considering g negative in the second case. In the potential energy calculation, we are taking h = (Reference point or surface of earth - height gained by body), which is negative. Two negatives cancel each other.
Thank u