Q 11-03-045JEE MainJEE Main 2026 (4 Apr, Shift 2)Medium
Two cars $A$ and $B$ are moving in the same direction along a straight line with speeds $100\ \text{km/h}$ and $80\ \text{km/h}$, respectively such that car $A$ is moving ahead of car $B$. A person in car $B$ throws a stone with a speed $v$ so that it hits the car $A$ with a speed of $5\ \text{m/s}$. The value of $v$ is ______ km/h.
Answer: (C) $38$
The stone must reach car $A$ with speed $5$ m/s $= 18$ km/h relative to $A$, so its ground speed is $100 + 18 = 118$ km/h.
It is thrown from car $B$ (moving at $80$ km/h), so its speed relative to $B$ is $v = 118 - 80 = 38$ km/h.
Solution by Sreeraj P, M.Sc Physics