3 Tutor System
Starting just at 265/hour

# Certain force acting on a 20 kg mass changes its velocity from 5 m/s to 2 m/s. Calculate the work done by the force.

Given,

Mass of the body = 20 kg

Initial velocity( u ) =5 m/s

Final velocity( v ) = 2 m/s

The initial kinetic energy

$$= E_i \ = \ \frac{mu^2}{2} \$$
$$= \ \frac{20 x (5)^2}{2} \$$
$$= \ 250 \ kgm/s^2$$

$$\therefore E_i \ = \ 250 \ J$$

Final kinetic energy

$$= E_f \ = \ \frac{mv^2}{2} \$$
$$= \ \frac{20 x (2)^2}{2} \$$
$$= \ 40 \ kgm/s^2$$

$$\therefore E_f \ = \ 40 \ J$$

$$\therefore Work \ done \ = \ Change \ in \ kinetic \ energy$$

$$\Rightarrow Work \ done \ = \ E_f \ – \ E_i$$

$$\Rightarrow Work \ done \ = \ 40 \ J \ – \ 250 \ J$$

$$\Rightarrow Work \ done \ = \ -210 \ J$$