Question

Certain force acting on a 20 kg mass changes its velocity from 5 m s^-1 to 2 m s^-1. Calculate the work done by the force.

Answer 1

Mass of the object, m = 20 kg

Total work done by the force = Change in the object's kinetic energy

= `1/2 mv^2 - 1/2 m u^2`

= `1/2 m (v^2 - u^2)`

u = 5ms⁻¹, u = 2ms⁻¹, m = 20 kg

= 4 × 5

= 20 

Hence, work done = `1/2m (v^2 - u^2)`

= `1/2 xx 20 [(2)^2 - (5)^2]`

= 10 × (−21)

= −210 J

The force will do work equivalent to 210 J. Here, the direction of force is opposite the direction of motion.