Question

A car runs at a constant speed on a circular track of radius 100 m, taking 62.8 s for every circular lap. The average velocity and average speed for each circular lap respectively is :

• A. 0, 0
• B. 0, 10 m/s
• C. 10 m/s, 20 m/s
• D. 20 m/s, 0

Answer 1

The Correct Option is B

100m is the lap radius.
Circumference = 2\(\pi\)R = 200\(\pi\) = 628 metres
It takes 62.8 seconds to complete one lap. 
Consequently, average speed =\(\frac{62.8}{628}\) = 10 m/s.
After finishing a lap, the initial and end positions are the same, hence the average velocity is 0 (displacement = 0).

Therefore, the correct option is (B): 0, 10 m/s

Answer 2

After making one turn on a circular path, the displacement is zero and the distance traveled is 2πr.
Hence, \(\text{average velocity} = \frac{\text{time-interval}}{\text{displacement}} = \frac{t_0}{0} = 0\)
\(\text{Average speed} = \frac{\text{Time-interval}}{\text{Distance}}\)

\(\text{Average speed} = \frac{t}{2\pi r} = \frac{62.8}{2 \times 3.14 \times 100} = 10 \text{ m/s}^{-1}\)