Question

A body moves with speed $V_{1}$ for distance $L$ and then with speed $V_{2}$ for distance $2L$ . The average speed for the motion is

• A. $\frac{V_{1} + V_{2}}{2}$
• B. $\frac{3 V_{1} V_{2}}{V_{1} + 2 V_{2}}$
• C. $\frac{3 V_{1} V_{2}}{2 V_{1} + V_{2}}$
• D. $\frac{3 V_{1} V_{2}}{V_{1} + V_{2}}$

Answer 1

Answer: (C)

Average speed $=\frac{\text{Total distance}}{\text{Total time}}$
$=\frac{3 L}{\frac{L}{V_{1}} + \frac{2 L}{V_{2}}}$
$=\frac{3 V_{1} V_{2}}{V_{2} + 2 V_{1}}$