Q7DQ - University Physics with Modern Physics

Question

In the conical pendulum of Example 5.20 (Section 5.4), which of the forces do work on the bob while it is swinging?

Step-by-Step Solution

Answer

No forces act on the bob of the conical pendulum when it is swinging.

Step 1: Describe the Work

The expression for the work is given by,

$\mathit{W}\mathbf{=}\overrightarrow{\mathbf{F}}\mathbf{.}\overrightarrow{\mathbf{s}}$ 

Here,$\overrightarrow{\mathbf{F}}$ is the force and $\overrightarrow{\mathbf{s}}$ is the displacement.

Step 2: Find the forces work on the bob while it is swinging

Draw the free-body diagram of conical pendulum

The centripetal force $\left(\frac{m{v}^2}{r}\right)$ and displacement of the pendulum is perpendicular to each other. So, centripetal force does not do work on the bob while it swinging.

 

The weight of the bob $\left(mg\right)$ and displacement of the pendulum are perpendicular to each other. So, the weight of the bob does not do work on the bob while it is swinging.

 

The tension $\left(T\right)$ in string and displacement of the bob made an angle $90°$. Hence, the tension $\left(T\right)$ does not work on the bob while it is swinging.

 

Therefore, no forces act on the bob of the conical pendulum when it is swinging