Multiple choice

A circular track has a circumference of 400 m. A and B run on the track at speeds 9 kmph and 5 kmph, respectively. If they start from a fixed point in the same direction, after what time will they be together again for the first time?

  1. 2 min

  2. 4 min

  3. 6 min

  4. 8 min

  5. None of these
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Relative speed = 9 - 5 = 4 kmph = 4 * (5/18) m/s = 10/9 m/s. Time to meet = Circumference / Relative speed = 400 / (10/9) = 360 seconds = 6 minutes.

AI explanation

Using the relative speed method for same-direction circular motion, the relative speed is 9 kmph minus 5 kmph, which equals 4 kmph. Converting this to meters per second gives 4 times 5/18, or 10/9 m/s. The time required to cover the 400 m gap at this relative speed is 400 divided by 10/9, resulting in 360 seconds, which is 6 minutes. The result is 6 min.

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