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?

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