A body of mass 4kg is acted on by a constant force of 12N for 3 seconds. The kinetic energy gained by the body at the end of the time is?

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A. 144J
B. 162J
C. 81J
D. 72J

Correct Answer:

Option B = 162J

Explanation

K.E = 1/2MV2
Force, F = ma => a = F/m = 12/4 = 3ms-2
But a = (V-U) / t => V = u + at
If the initial velocity U = 0, then V = at = 3 x 3 = 9ms-2
∴ K.E, = 1/2ms-2
1/2 4 x 9 x 9 = 162J

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