Q. One car moving on a straight road covers one third of the distance with $20\ km/hr$ and the rest with $60\ km/hr$. The average speed is
A) $40\ km/hr$
B) $80\ km/hr$
C) $46\frac{2}{3}\ km/hr$
D) $36\ km/hr$
Explanation
(d) Average speed $= - \frac{Total\ distance}{Total\ time} = \frac{x}{t_{1} + t_{2}}$
$= \frac{x}{\frac{x/3}{v_{1}} + \frac{2x/3}{v_{2}}} = \frac{1}{\frac{1}{3 \times 20} + \frac{2}{3 \times 60}} = 36\ km/hr$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.