question_answer 28)

Two persons manage to push a motorcar of mass 1200 kg at a uniform velocity along a level road. The same motorcar can be pushed by three persons to produce an acceleration of 0.2 m s-2. With what force does each person push the motorcar? (Assume that all persons push the motorcar with the same muscular effort.)  

Answer:

Here, mass of motorcar, m = 1200 kg Let each person exert a push F on the motorcar. Total push of two persons = F + F = 2 F                                                  As this push gives a uniform velocity to the motocar along a level road, it must be a measure of the force of friction (f) between the motorcar and the road, i.e., f = 2F When three person push, total force applied F + F + F = 3F                            Force that produces acceleration (a = 0.2 m s-2), i.e., Ma = 3 F – f = 3 F - 2 F = F or F = ma = 1200 x 0.2 = 240 N