Suppose each person applies a force F to push the motorcar.
So, Total force applied by two persons=F+ F
Since this force (2F) gives a uniform velocity to the motorcar along a level road (where work is done only against the force of friction), so the force 2F can be taken as being equal to the force of friction f between the motorcar and the road. That is,
Force of friction, f=2F ....(2)
Now, when three persons apply force to push the motorcar, then:
Total force applied by three persons=F+ F+F
Now, the total force applied by three persons is 3F whereas the opposing force of friction is f. So,
Force that produces acceleration=3F-2F ...(4)
But from equation (2), we have f=2F.So,
Force that produces acceleration=3F-2F
or Force that produces acceleration=F
Now, Force =mass `xx` acceleration
Thus, each person pushes the motorcar with a force of 240 newtons.