Multiple choice

A person walking at the speed of 3 km/hr was overtaken by a carriage. It being a foggy day, the sight distance was limited to 100 metres. The person was able to see the carriage for 30 seconds only. Find the speed of the carriage.

  1. 21 km/hr

  2. 19 km/hr

  3. 16 km/hr

  4. 15 km/hr
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D Correct answer
Explanation

The relative speed of the carriage with respect to the person is distance / time = 100 m / 30 s = 10/3 m/s. Converting to km/hr: (10/3) * (18/5) = 12 km/hr. Since the carriage overtakes the person, the carriage speed = person speed + relative speed = 3 + 12 = 15 km/hr.

AI explanation

The relative speed is used when a carriage overtakes a person, calculated by dividing the sight distance by the visible time. Converting 100 metres to 0.1 kilometres and 30 seconds to 1 over 120 hours, the relative speed is 0.1 divided by 1 over 120, yielding 12 km/hr. Adding this relative speed to the person's walking speed of 3 km/hr gives the carriage's speed of 15 km/hr.

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