Question

A man travels half length of a straight road with a constant speed of 20 ${m} / {sec}$, and he travels the second half length of the road with a constant speed of $60 {m} / {sec}$, then calculate its average speed.

Answer 1

ANSWER : $30 {~m} / {sec}$.

SOLUTION —

Let the total distance travelled $={L}$

Hence, total time taken $=\frac{L / 2}{20}+\frac{L / 2}{60}$

$\therefore \quad \text { Average Speed } =\frac{\text { Total distance travelled }}{\text { Total time taken }}$

$=\frac{L}{\frac{L / 2}{20}+\frac{L / 2}{60}}=\frac{40 \times 120}{160}=30 {m} / {sec}$