Question

A body moves with a speed of $20\text{kmph}$ in the first $5\text{s}$ and with a speed of $30\text{kmph}$ in the next $5\text{s.}$ Then, the average speed of the body is :

• A. $25\text{kmph}$
• B. $24\text{kmph}$
• C. $0\text{kmph}$
• D. $10\text{kmph}$

Answer 1

The correct option is A $25\text{kmph}$

Average speed $=\frac{\text{Total Distance}}{\text{Total time}}$

Distance travelled in $5\text{s}$ with speed $20\text{kmph}=\frac{5}{3600}\times 20\text{km}$

Distance travelled in $5\text{s}$ with speed $30\text{kmph}=\frac{5}{3600}\times 30\text{km}$

So, the total distance travelled in 10s $=\frac{5}{3600}\times 50\text{km}$

Total time $=10s=\frac{10}{3600}\text{hrs}$

Average speed $=\frac{250}{3600}\times \frac{3600}{10}=\frac{250}{10}=25\text{kmph}$