A body of mass 5 kg, initially at rest, is subjected to a force of 20N. What is the kinetic energy acquired by the body at the end of 10 s ?

2000 J

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4000 J

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8000 J

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1000 J

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Solution

The correct option is A $4000 J$
Given, mass of the body, $m = 5 k g$ ;
Initial velocity of the body, $u = 0$ ;
Force acting on the body, $F = 20 N$ ;
Time for which the force acts, $t = 10 s$
If $a$ is the acceleration produced in the body,
$a = \frac{F}{m} = \frac{20}{5} = 4 m / s^{2}$
Let v be the velocity of the body after 10 s.
Clearly, $v = u + a t = 0 + (4) \times (10) = 40 m / s$
Kinetic energy acquired by the body,
$E_{k} = \frac{1}{2} m v^{2} = \frac{1}{2} (5) \times (40)^{2} = 4000 J$

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