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A body of mass 4kg is acted on by a constant force of 12N for 3 seconds. The kin...


Question

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

Options

A) 144J

B) 162J

C) 81J

D) 72J


The correct answer is B.

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-21/2 4 x 9 x 9 = 162J

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Dicussion (1)

  • 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-21/2 4 x 9 x 9 = 162J

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