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Question
A metal ball of mass 2 kg is allowed to fall freely from rest from a height of 5 m above the ground. Taking g = 10 m s−2, calculate:
- the potential energy possessed by the ball when it is initially at rest.
- the kinetic energy of the ball just before it hits the ground?
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Solution
Mass of the ball m = 2 kg, g = 10 ms−2, h = 5 m
(i) Potential Energy possessed by the ball = mgh
= 2 × 10 × 5
= 100 J
(ii) K.E of ball = potential Energy = 100 J
or v2 = 2gh
v2 = 2 × 10 × 5
= 100 J
∴ K.E = `1/2 mv^2`
= `1/2 xx 2 xx 100`
= 100 J
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