Question

A body goes from A to B with a speed of 20 m/s and comes back to A with a speed of 30 m/s. The average speed of the body during the whole journey is:

• A. zero
• B. 24 m/s
• C. 25 m/s
• D. 23 m/s

Answer 1

The correct option is B 24 m/s

Let the body goes from A to B in $t_1$ sec and comes back from B to A in $t_2$ sec. and let the distance between A and B be s.
$\therefore t_1=\frac{s}{20}$
and $t_2=\frac{s}{30}$
Total distance traveled $=s+s=2s$
Total time taken $=t_1+t_2$
$=\frac{s}{20}+\frac{s}{30}=\frac{5s}{60}$
$\therefore$ Average velocity $=\frac{2s}{t_1+t_2}$
Putting the values, we get average speed = $24m/s$