Question

A 5 Kg box is kept on a rough horizontal surface and another 1 kg box is kept on a smooth horizontal surface. Which of the following statement is true?

• A. 5 Kg box has higher frictional force compared to 1 kg box.
• B. 1 Kg box has higher frictional force compared to 5 kg box.
• C. Both boxes have zero frictional forces.
• D. Frictional force on the blocks will depend on the roughness and smoothness of the contacting surfaces.

Answer 1

The correct option is C Both boxes have zero frictional forces.

Frictional force will be applicable only when two surfaces in contact try to do relative motion with respect to each other. Here, there is no external horizontal force on the blocks. So there is no attempt of any relative motion. So frictional forces on both the blocks are zero.