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

• A. 2.8 joules
• B. 3.2 joules
• C. 3.8 joules
• D. 4.4 joules

Answer 1

Answer: (D)

Change in momentum = Force $\times$ 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 $K.E.$
$=\frac{1}{2m}\left(P^{2}_{2}-P_{1}^{2}\right)$
$=\frac{1}{2\times5}\left[\left(12\right)^{2}-\left(10\right)^{2}\right]$
$=\frac{44}{10}=4.4\, J$