Question

Question 5.8 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.

Chapter Laws Of Motion Page 110

Answer 1

Acceleration=v-u/t
V= 0, u= 36 or 36×5÷18=10m/s,t= 4 s
A= -10/4=-5/2,Mass= 465kg
Force= 465×-5/2=-1162.5N

Answer 2

Speed of driver = 36 km/h
= 36 × 5/18 m/s
= 10 m/s
After applying break he comes to rest in 4sec .
So, final velocity = 0
Use formula ,
V = U + at
0 = 10 + a× 4
a = -2.5 m/s²
Here negative sign indicates that body was regarding .
Now, regarding force = ma
Mass of body = 65 Kg
a = -2.5 m/s²
So,
Regarding force = 65×(-2.5)N
= -1162.5 N