A motorcar of mass 1200 kg is moving along a straight line with a uniform velocity 90 `km h^(-1)` is slowed down to 18 `km h^(-1)` in 4s by an unbalanced external force. Calculate the acceleration and change in momentum . Also calculate the magnitude of the force required .

Explanation

Here,m=1200kg
u=90 km `h^(-1)`
`=90xx(5)/(18)ms^(-1)=25 ms^(-1)`
`v=19 km h^(-1)=18=(5)/(18) ms^(-1)=5 ms^(-1),t=4s`
Acceleration `a=(v-u)/(t)=(5-25)/(5)ms^(-1)=-5 ms^(-2)`
`rarr` change in the momentum of the car F=ma=`1200xx(-5)N=-6000N`
Negative sign of acceleration and change in the momentum and force suggest that the force is opposing the magnitude of the car.
The magnitude of the force required is 6000N