The driver of a three-wheeler moving at 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 velocity, \( u= 36 km/h \)
Final velocity, \( v = 0 \)
Mass of the three-wheeler, \( m_1= 400 Kg \)
Mass of the driver, \( m_2 = 65 Kg \)
Time taken to bring the vehicle to rest = 4.0 s
\( Acceleration,\ a = v- u/t = (0 – 10)/ 4 =\ – 2.5 m/s \)
\( Now,\ F = (m1 + m2)/ a = (400 + 65) \times (-2.5) \)
\( =\ – 1162.5 N =\ – 1.16 \times 10^3 N. \)
The negative sign shows that the force is retarding.
The average retarding force on the vehicle is \( – 1.16 \times 10^3 N. \)