Certain force acting on a 20 kg mass changes its velocity

Solution:

Given, mass, $\mathrm{m}=20 \mathrm{~kg}$;

initial velocity, $\mathrm{u}=5 \mathrm{~ms}^{-1}$;

final velocity, $\mathrm{v}=2 \mathrm{~ms}^{-1}$

Work done by the force = change in kinetic energy

or $W=\frac{1}{2} m v^{2}-\frac{1}{2} m u^{2}=\frac{1}{2} m\left(v^{2}-u^{2}\right)$

or $\mathbf{W}=\frac{1}{3}(20)\left((2)^{2}-(5)^{2}\right]=-210 \mathbf{J}$.