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.
Given: Initial speed of the three-wheeler, u=36km/h=10m/s Final speed of the three-wheeler, v=0 m/s Time, t=4s Mass of the three-wheeler, m=400 kg Mass of the driver, m′=65kg Total mass of the system, M=400+65=465 kg Using the first law of motion, the acceleration (a) of the three-wheeler can be calculated as: v=u+at a=t(v−u)=4(0−10)=−2.5m/s2 The negative sign indicates that the velocity of the three-wheeler is decreasing with time. Using Newton's second law of motion, the net force acting on the three-wheeler can be calculated as: F=Ma=465×(−2.5)=−1162.5N The negative sign indicates that the force is acting against the direction of motion of the three-wheeler.
