Question

A `1200` `kg` object moves `200` `m` at constant velocity in `20` `s`. It requires a driving force of `600` `N` to maintain this motion against friction and air resistance. What power is exerted by the driving force?

Answer 1

Driving force `= 600` `N`
Work done `=120,000` `J`
Power `=12,000` `W`

Explanation:

The resisting frictional force will be given by `1200` `kg` times `0.5` `Nkg^-1 = 600` `N`. Since the velocity is constant, the driving force will be exactly equal to the frictional force: `600` `N`.

The work is given by `W=Fd=600xx200=120,000` `J=120` `kJ`.

To find the power we need to know the time taken for the motion:

`v=s/t`

Rearranging:

`t=s/v=200/20=10` `s`

Then power is given by:

`P=W/t=(120,000)/10 = 12,000` `W = 12` `kW`