Q. You drive a car at seed of $\ 70\ km/hr$ in a straight road for $8.4\ km,$ and then the car runs out of petrol. You walk for $30\ min$ to reach a petrol pump at a distance of $2\ km$. The average velocity from the beginning of your drive till you reach the petrol pump is
A) $16.8\ km/hr$
B) $35\ km/hr$
C) $64\ km/hr$
D) $18.6\ km/hr$
Explanation
(a) [image:3_image182.emf]
Average speed $\overline{v} = \frac{Total\ distance\ travelled}{Total\ time\ taken}$
$= \frac{8.4km + 2km}{t_{1} + t_{2}} = \frac{10.4\ km}{\left( \frac{8.4\ km}{70\ km/h} \right) + \frac{1}{2}h}$
$= \frac{10.4\ km}{0.12h + 0.5h} = 16.8\ km/h$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.