Question

Work done is said to be negative, when a force causes displacement:

• A. in the direction opposite to the direction of applied force
• B. in the direction of applied force
• C. in the direction at right angles to the direction of applied force
• D. none of the above

Answer 1

The correct option is A

in the direction opposite to the direction of applied force

However, if we consider the forces acting on the block in totality, then there is the force of friction (F) acting at an angle of ${180}^0$ to the applied force.

1. In such a situation, the work done by the force of friction will be:
2. $\therefore W=-F\times s$
3. The minus sign indicates that the force is acting opposite to the direction of displacement.
4. Thus, the work done by the force of friction is negative.

Hence, option A is correct.