Question

An ant completes moving along a circle in 5 seconds with a constant speed, total time taken by it to travel along the diameter and come back is

• A. 10 s
• B. 3.18 s
• C. 6.36 s
• D. 5.26 s

Answer 1

The correct option is B 3.18 s

Let radius of the circle be r.

In the first case, distance travelled = $2\pi r$, and time taken, $t_1$ = 5 s
In the second case, distance travelled = 4r, and let the time taken be $t_2$.
We know, $distance=speed\times time$
As speed of ant is constant, $time\propto distance$
$\therefore$ $\frac{t_2}{t_1}$ = $\frac{4r}{2\pi r}$.
$\Rightarrow$ $t_2$= $\frac{4r}{2\pi r}\times 5$
= $\frac{2}{\pi }\times 5$
= 3.18 s