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

Explanation

Here mass m=1200 kg
Initial velocity `u=90 km h^-1`
`=90 times 5/18=25 ms^-1`
Final velocity `v=18 km h^-1`
`=18 times 5/18=5 ms^-1`
Time t=4s
(i) Acceleration a = `("chang e i n velocity")/("Time")`
`=(v-u)/t=(5-25)/4=-5 ms^-2`
(ii) change in momentum
=`mv-mu=m(v-u)`
=`1200 (5-25)`
`=-24000 kg ms^-1`
Magnitude of change in momentum
`=24000 kg ms^-1`
(iii) Force `F=ma=1200 (-5) =-6000 N`
`therefore` Magnitude of force =6000 N