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.
Initial speed of the three-wheeler, u = 36 km/h = 10 m/s
Final speed of the three-wheeler, v
= 0 m/s
= 4 s
Mass of the three-wheeler, m
= 400 kg
Mass of the driver, m
' = 65 kg
Total mass of the system, M
= 400 + 65 = 465 kg
According to the first law of motion,
) of the three-wheeler is, v = u + at
The negative sign indicates that the velocity of the three-wheeler is decreasing with time.
Now, using Newton’s second law of motion, the net force acting on the three-wheeler is, F
= 465 × (–2.5)
= –1162.5 N
The negative sign indicates that the force is acting against the direction of motion of the three wheeler.