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Question

A body of mass 5 kg is moving with a momentum of 10 kg-m/s. A force of 0.2 N acts on it in the direction of motion of the body for 10 seconds. The increase in its kinetic energy is (in J)

Moderate

Solution

Change in momentum = Force × time
$P_{2} - P_{1} = F \times t = 0 .2 \times 10 = 2$
$\Rightarrow P_{2} = 2 + P_{1} = 2 + 10 = 12 kg - m / s$
Increase in K.E. = $\frac{1}{2 m} (P_{2}^{2} - P_{1}^{2}) = \frac{1}{2 \times 5} [{(12)}^{2} - {(10)}^{2}]$
$= \frac{44}{10} = 4 .4 J$

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