Question

8.The driver of a car moving with a velocity 40 km/h sees a child standing in the middle of the road and brings the car to rest in 5 s just in time to save the child. The average retarding force on the car is: a)1000 N b)1266 N c)1400 N d)800 N

Answer 1

Explanation:

Initial velocity, u = 40 km/h = 40 x (5/18) = 200/18 m/s

Final velocity, v= 0

Distance travelled before coming to rest, S = 2 m

Using, v2 = u2 + 2as

=> a = -u2/(2s)

=> a = -30.864 m/s2

Again,

u = 80 km/h = 400/18 m/s

V = 0

a = -30.864m/s2

Now, v2 = u2 + 2as

=> S = -u2/(2a) = 8 m