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JEE Main20264 April 2026Evening ShiftPhysicsMotion in One DimensionActual

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 5 m/s. The value of v is ______ km/h.

Options

  1. A18
  2. B28
  3. C38
  4. D48

Correct answer

C. 38

Step-by-step solution

Velocity of car A, v_A = 100 km/h Velocity of car B, v_B = 80 km/h Velocity of the stone relative to car B is v . The velocity of the stone relative to the ground is v_S = v_B + v = 80 + v . The velocity of the stone relative to car A is v_ S/A = v_S - v_A = (80 + v) - 100 = v - 20 . The stone hits car A with a relative speed of 5 m/s. Converting this speed to km/h: v_ S/A = 5 18 5 = 18 km/h Equating the relative speeds: v - 20 = 18 v = 38 km/h Answer: 38

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