Question

A man runs around a circular track of 800 meters radius for 30 seconds, starting at a point directly to the right of the center and goes in a counterclockwise manner. He goes 5 meters per second for the first 15 seconds, runs 90 meters for the next 6 seconds and then 180 meters for the rest of the course. What was his average speed?

Answer 1

Explanations & Calculations

• The total distance he would have covered during the course is

$\qquad\qquad \begin{aligned} \small S&=\small (5\,ms^{-1}\times15\,s)+(90\,m)+(180\,m)\\ &=\small 345\,m \end{aligned}$

• Total time he would have taken is

$\qquad\qquad \begin{aligned} \small t&=\small 30\,s \end{aligned}$

• Then the average speed would be

$\qquad\qquad \begin{aligned} \small Avg.speed&=\small \frac{Distance}{time}\\ &=\small \frac{345\,m}{30\,s}\\ &=\small 11.5\,ms^{-1} \end{aligned}$

• He did not cover the whole circle ($\small L= 2\pi.800)$ during that time.