Q. Two cars $A\ and\ B$ are moving with same speed of $45\ {kmh}^{- 1}$ along same direction. If a third car $C$ coming from the opposite direction with a speed of $36\ {kmh}^{- 1}$ meets two cars in an interval of 5 min, the distance of separation of two cars $A\ and\ B$ should be (in km)
A) 6.75
B) 7.25
C) 5.55
D) 8.35
Explanation
(a) $v_{rel} = 45 + 36 = 81\ {kmh}^{- 1} = 81 \times \frac{5}{18}{ms}^{- 1}$
$\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ s_{rel} = v_{rel} \times t = 81 \times \frac{5}{18} \times (5 \times 60)$
$\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ = \frac{81 \times 5 \times 5 \times 60}{18} - 6750\ m = 6.75\ km$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.