Question

A block of mass $m$, kept on a horizontal surface, is moved through a distance $s$ by applying a horizontal force $F$ to it. What is the work done by the normal reaction?

• A. $\dfrac{F}{s}$
• B. $Fs$
• C. zero
• D. $\dfrac{s}{F}$

Hint:

If force is perpendicular to displacement, the work done is always zero.

Answer 1

The Correct Option is C

Step 1: Direction of normal reaction.
Normal reaction acts vertically upward.

Step 2: Direction of displacement.
The displacement of the block is horizontal.

Step 3: Work done formula.
\[ W = Fs\cos\theta \]
Step 4: Angle between force and displacement.
For normal reaction, $\theta = 90^\circ$.
\[ \cos 90^\circ = 0 \]
Step 5: Conclusion.
Work done by the normal reaction is zero.