Question

An athlete running with constant speed, completes one round of a circular track of radius $R$ in $40\text{seconds}$. What will be his angular displacement at the end of $20\text{seconds}$?

• A. $\frac{\pi }{2}\text{rad}$
• B. $\frac{\pi }{3}\text{rad}$
• C. $\frac{\pi }{4}\text{rad}$
• D. $\pi \text{rad}$

Answer 1

The correct option is D $\pi \text{rad}$

If athlete completes one round of a circular track of radius $R$ in $40\text{seconds}$ then,
After $20\text{seconds},$
No. of rounds completed $=\frac{20}{40}=0.5$
Athlete will cover half of the circle.
Therefore, angular displacement after completing half rounds $=\frac{2\pi }{2}\text{rad}=\pi \text{rad}$