Q. If a car covers $2/5^{th}$ of the total distance with $v_{1}$ speed and $3/5^{th}$ distance with $v_{2}$ then average speed is
A) $\frac{1}{2}\sqrt{v_{1}v_{2}}$
B) $\frac{v_{1} + v_{2}}{2}$
C) $\frac{2v_{1}v_{2}}{v_{1} + v_{2}}$
D) $\frac{5v_{1}v_{2}}{3v_{1} + 2v_{2}}$
Explanation
(d) $Average\ speed = \frac{Total\ distance\ travelled}{Total\ time\ taken}$
$= \frac{x}{\frac{2x/5}{v_{1}} + \frac{3x/5}{v_{2}}} = \frac{5v_{1}v_{2}}{3v_{1} + 2v_{2}}$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.