A body of mass 4 kg is moving with momentum of 8 kg ${\mathrm{ms}}^{-1}$. A force of 0.2 N acts on it in the direction of motion of the body for 10s. The increase in kinetic energy is

Momentum = mass $\times$ velocity $\Rightarrow \mathrm{p} = \mathrm{mu}$

or  u = $\frac{\mathrm{p}}{\mathrm{m}} = \frac{8 \mathrm{kg} {\mathrm{ms}}^{-1}}{4 \mathrm{kg}} = 2 {\mathrm{ms}}^{-1}$

Acceleration = $\frac{\mathrm{Force}}{\mathrm{Mass}}$

a = $\frac{0.2 \mathrm{N}}{4 \mathrm{kg}} = 0.05 {\mathrm{ms}}^{-2}$

Distance travelled by the body in 10 s is

d = $\mathrm{ut} + \frac{1}{2}{\mathrm{at}}^2$

    = $(2 {\mathrm{ms}}^{-1})(10 \mathrm{s})+\frac{1}{2}(0.05 {\mathrm{ms}}^{-2}){(10 \mathrm{s})}^2$

    = 20 m + 2.5 m = 22.5 m

Work done, W = Fd = (0.2 N)(22.5 m) = 4.5 J

According to work-energy theorem

Increase in kinetic energy = Work done = 4.5 J