Question

No work is done when

• A. a nail is plugged into a wooden board
• B. a box is pushed along a horizontal floor
• C. there is no component of force parallel to the direction of motion
• D. there is no component of force normal to the direction of motion.

Answer 1

The correct option is C

there is no component of force parallel to the direction of motion

Explanation for correct option:

(C) there is no component of force parallel to the direction of motion

1. When there is no component of force in the direction of motion, then force is not applied in the direction of motion.
2. When the force applied in the direction of motion is zero, then work done in the direction of motion is zero.

Explanation for incorrect options:

(A) a nail is plugged into a wooden board

1. When a nail is plugged into a wooden board, a force is applied and the nail moves through a certain distance.
2. Since the nail moves through a certain distance under the effect of a force applied in the same direction as the motion, therefore, work is done.

(B) a box is pushed along a horizontal floor

1. When a box is pushed on a horizontal floor, a force is applied to it and the box moves through a certain distance.
2. Since the box moves through a certain distance under the effect of a force applied in the same direction as the motion, therefore, work is done.

(D) there is no component of force normal to the direction of motion.

1. When the direction of force is different from the direction of motion, work done is given as, $W=FS\cos \theta$, where, $F$ is force, $S$ is distance and $\theta$ is the angle between the direction of force and the direction of displacement.
2. When the force is applied normal to the direction of motion, work done will be $W=FS\cos 90°=FS\times 0=0$.
3. Since there is no component of force normal to the direction of motion, work will be done

Therefore, no work will be done when there is no component of force parallel to the direction of motion. Hence option (C) is correct.