Question

Work done by normal reaction is zero during the motion of the block:

A) From point A to B only
B) From point B to C only
C) From A to C
D) None of these

Answer 1

Hint: In order to solve this question you have to remember the concepts of the work-energy theorem and the use of force for finding work done. The work-energy theorem states that the work done by all the forces that are acting on a particle will be equal to the change in the kinetic energy of that particle.

Complete step by step solution:
In the question, it is given a small block of mass m, which is released from point A on a fixed smooth wedge as shown in the above figure. The top of the wedge is marked as A and the bottom as B and at point C the block stops moving because of the roughness of the floor.
We have to find the portion where the work done by the normal reaction is zero during the motion of the block

We already know that the normal reaction is always perpendicular to the direction of motion.
So, it means that the work done by the normal reaction is equal to zero from point A to C as the normal reaction is perpendicular to the displacement of the block.
Hence, from the above discussion, it is clear that the work done by the normal reaction is zero during the motion of the block will be from point A to C.

Therefore, the correct option is (C).

Note: Always keep in mind that the normal reaction is the force that is applied by the surface in reaction to the weight that the object exerts on the surface. The normal reaction force is perpendicular to the surface that an object contacts. For example, the table surface that prevents an object from falling from the table.