A motor car is moving with a velocity of `108 km//h` and it takes `4 second` to stop after the brakes are applied. Calculate the force exerted by the brakes on the motorcar if its mass along with the passenger is `1000 kg`.

Explanation

The initial velocity of motorcar
`u=108 km//h`
`=108xx1000 m//(60xx60s)`
`=30 ms^(-)`
and the final velocity of the motorcar ` v=0 ms^(-1)`.
The total mass of the motorcar along with its passangers= 1000 kg and the time taken to stop the motorcar, t=4s. From Eq. (9.5) we have the magnitude of the force (F) applied by the brakes as m(v-u)/t.
On substituting the values, we get` F=1000 kg xx (0-30) ms^(-1)//4s`
=`-7500 kg ms^(-2) " or " -7500 N.` . The negative sign tells us that the force exerted by the brakes is opposite to the direction of motion of the motorcar.