Multiple choice

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)

  1. 30.5 ms-1

  2. 29.5 ms-1

  3. 31.5 ms-1

  4. 28.5 ms-1
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Train A speed is 10 m/s, Train B speed is 20 m/s. The person in Train A moves at 0.5 m/s opposite to the train, so their ground speed is 10 - 0.5 = 9.5 m/s. Relative to Train B (moving in opposite direction), the speed is 9.5 + 20 = 29.5 m/s.

AI explanation

The velocity of the person with respect to the ground is determined by subtracting the person's walking speed from train A's speed: 36 km/hr - 1.8 km/hr = 34.2 km/hr in the direction of train A. Train B is moving towards train A at 72 km/hr, so the relative speed of the person as observed from train B is the sum of their opposite velocities: 34.2 km/hr + 72 km/hr = 106.2 km/hr. To convert this to meters per second, multiply by 5/18, which gives 106.2 * (5 / 18) = 29.5 m/s. The speed of the person as observed from train B is 29.5 m/s.

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