Question

When a men walks on a horizontal surface then work done by

• A. friciton is zero
• B. contact force is non-zero
• C. gravity is non-zero
• D. None of these

Answer 1

The correct option is B contact force is non-zero

When the man moves on a horizontal surface, then work done by gravity is zero since gravitational force acts perpendicular to the displacement.

And the normal force will be also perpendicular to displacement so work done by It also is zero. - - - - - - - - 1

But frictional force is acting opposite to displacement so work done by frictional force is negative. - - - - - - - - - - - 2

Using statement (1) and (2) we can say that work done by contact force is non - zero