Question

When brakes are applied to a moving vehicle, the work done by the braking force is

• A. Zero
• B. Positive
• C. Negative
• D. Unity

Answer 1

The correct option is C

Negative

We know that work done,$W=FS\cos \theta$

where $F=$force acted, $S=$displacement and $\theta =$gradient between the direction of force and displacement of the body.

Since the braking force acts in the backward direction while the displacement of the vehicle is in the forward direction.

So, as $\theta ={180}^{\circ }thenCos180=-1$

$$\begin{gathered} \therefore W=FS\times \left(-1\right) \\ W=-FS \end{gathered}$$

Thus, work done by the braking force is negative.

Hence, option (c) is correct.