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JEE Main 2020 (2 Sep, Shift 1) · Relative Velocity

Relative Velocity question from JEE Main 2020 (2 Sep, Shift 1)

Q8JEE Main 2020 · 2 SEP · SHIFT 1Easy

Relative Velocity

Train A and train B are running on parallel tracks in the opposite directions with speeds of 36 km/hour and 72 km/hour, respectively. A person is walking in train A in the direction opposite to its motion with a speed of 1.8 km/ hour. Speed (in ms–1) of this person as observed from train B will be close to:

(take the distance between the tracks as negligible)

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Answer: (b)

  1. vA=36 km/h=10 m/sv_A = 36\text{ km/h} = 10\text{ m/s}, person relative to A =−1.8 km/h=−0.5 m/s= -1.8\text{ km/h} = -0.5\text{ m/s}, vB=−72 km/h=−20 m/sv_B = -72\text{ km/h} = -20\text{ m/s}
  2. Person w.r.t. ground: 10−0.5=9.5 m/s10 - 0.5 = 9.5\text{ m/s}
  3. Person w.r.t. B: 9.5−(−20)=29.5 m/s9.5 - (-20) = 29.5\text{ m/s}
  4. So the answer is (b) 29.5 m/s.
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