Question

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

Answer 1

First, 

There is uniform velocity. This means no acceleration. This means net force will be zero (according to first law)

So, the applied force = Friction Force

F + F = f

2F = f

In second case

F+F+F -f = m a

3F- 2F = 1200 x 0.2

F = 240 N