A lorry and a car moving with the same kinetic energy are brought to rest by the application of brakes which provides equal retarding forces. Which of them will come to rest in a shorter distance?

Explanation

(a) Initial kinetic energy of each vehicle is K and when they come to rest their final kinetic energy is zero, The change in kinetic energy of both the car and lorry is K.By work - energy theorem
FS = change in kinetic energy FS = K, `S = (K)/(F)`
where F is the retarding force. As K and F are same for both the vehicles, they come t rest after travelling the same distance.
(b) To find the time in which each vehicle comes to rest, we have to consider the momentum,
`p=sqrt(2mxxK)"since" K = (p^(2))/(2m)`
The intial momentum of the car is less than that of the lorry as K is same for both but mas of car is less than that of the lorry. Final momentum is zero for both the vehicles, So, changes is momentum is lesss for the car By Newton.s second law,
`F=(Deltap)/(Deltat),Deltat=(Deltap)/(F)`
Since .F. is same, `Deltat propDeltap`
As car has smaller momentum, the car comes to rest earlier.