Q.7 Iqbal has to push a lighter box and Seema has to push a similar heavier box on the same floor. Who will have to apply a larger force and why?

Iqbal has to push a lighter box, so the interlocking between the surface of the lighter box and the surface of the floor is comparatively less than that of the heavier box. Because lighter box has less mass, so its' surface's roughness gets less pressed into the surface's roughness of the floor, thus making the interlocking less stronger and easier to overcome the friction using an external force of push.

While Seema has to push a similar heavier box, so the interlocking between the surface of the heavier box and the surface of the floor is comparatively more than that of the lighter box. Because heavier box has more mass, so its' surface's roughness gets more pressed into the surface's roughness of the floor, thus making the interlocking more stronger and harder to overcome the friction using an external force of push.

So Seema will have to apply a larger force.