JEE Main 2026 — Apr 4, Shift 2 — Physics solution

JEE Main2026Apr 4, Shift 2Physics

Two cars A and B are moving in the same direction along a straight line with speeds 100 km/h and 80 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 5m/s. The value of v is ________ km/h.

A
18
B
28
C
38
D
48

Solution

Convert the impact speed first: $5 m/s = 5 \times \frac{18}{5} = 18 km/h$ . This is the speed of the stone relative to car A at impact.

Let $v$ be the stone's speed (in km/h) relative to car B, in the forward direction. The stone's ground speed is then $v + 80$ .

Relative to car A, the stone's speed is $(v + 80) - 100 = v - 20$ .

Setting this equal to 18 km/h: $v - 20 = 18 \Rightarrow v = 38$ km/h.

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