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

Explanation

The work done by the force will be equal to the change in kinetic energy when the velocity changes from `5 m s^(-1)` to `2 m s^(-1)`.
(i) In the first case :
Mass, m = 20 kg
And Velocity, `v = 5 m s^(-1)`
`K.E. = (1)/(2) mv^(2)`
`= (1)/(2) xx 20 xx (5)^(2)`
`= (1)/(2) xx 20 xx 25`
`= 250 J" "...(1)`
(ii) In the second case :
Mass, m = 20 kg
And Velocity, `v = 2 m s^(-1)`
So, `K.E. = (1)/(2) mv^(2)`
`= (1)/(2) xx 20 xx (2)^(2)`
`= (1)/(2) xx 20 xx 4`
`= 40 J" "...(2)`
Work done by force = Change in kinetic energy
`= 250 - 40 J`
= 210 J