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.

Answers (1)

Total mass of the system = 400 + 65 = 425 kg

Using first law of motion, we get

                                  v = u + at

Since the car comes to rest, thus final velocity will be zero.

                                  0 = 10 + a(4)

or                              

                             a = frac-104 = -2.5 m/s^2

So the force required :

                                            F = ma

or                                                = 465	imes (-2.5)

or                                         F = -1162.5 N

So the magnitude of the force is 1162.5 N and it is retarding force.    

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