Question

A boy is moving at a speed of $2\text{m/sec}$ for $10$ minutes and then at $4\text{m/sec}$ for next $10$ minutes. The average speed of the boy is

• A. $4\text{m/sec}$
• B. $3\text{m/sec}$
• C. $6\text{m/sec}$
• D. $2\text{m/sec}$

Answer 1

The correct option is B $3\text{m/sec}$

Boy travels for $10$ minutes with speed of $2\text{m/sec}$
Then, distance travelled $=10\text{min}\times 60\times 2\text{m/s}=1200\text{m}$
And also, travels $10$ minutes with speed of $4\text{m/sec}$
Again, distance travelled $=4\text{m/s}\times 10\text{min}\times 60=2400\text{m}$
$\therefore$ Averege speed $=\frac{\text{Total Distance}}{\text{Total Time}}$
$=\frac{3600\text{m}}{20\times 60\left(s\right)}=3\text{m/sec}$