Question

two men try to push a heavy box and could not succeed finally wheels were fitted to the box and now a single man could move it justify

Answer 1

That's because the friction was more when the box was pushed. When wheels were added, sliding friction changes to rolling friction which is why it became easy for a single man to move it.

Answer 2

Answer:

Explanation: Moving the box just like thet increases friction. But when you put wheels to the box or keep the box on a cart(or something like that)....the wheels decrease friction,thereby making the box easy to move.That is the reason of a single man moving the box wuth wheels.