question_answer

      A large box, placed on the ground, has to be shifted up to a wall, as shown in the given figure. Three boys push the box together. They have to apply a large amount of force to move the box. The motion of the box is opposed by the frictional force between the box and the ground. If wheels were present below the box, then they would have to apply (a) More force                  (b) Same force (c) Less force                     (d) No force

Answer:

Here, the student is required to determine the change in the amount of force required when the box moves over wheels. Since frictional force opposes the motion of the box, the boys have to apply a large amount of force. If wheels were present below the box, then the frictional force between the box and the surface would decrease.