The driver of a three-wheeler moving with a speed of 36 km/h sees a child standing in the middle of the road and brings his vehicle to rest in 4.0 s just in time to save the child. What is the average retarding force on the vehicle ? The mass of the three-wheeler is 400 kg and the mass of the driver is 65 kg.

Explanation

Initial velocity of vehicle
`v_(0) = 36 km//h = (36 xx 1000)/( 3600)`
final velocity v= 0
total mass of vehicle and driver
m= 400+ 55
Retarding force on vehicle
F= ma
`=- 1162 .5 N` magnitude 1162 N