- Speed of the man in still water = 7 1/2 km/hr = 15/2 km/hr. - Speed of the stream = 1 1/2 km/hr = 3/2 km/hr. - Speed downstream = Speed in still water + Speed of stream = 15/2 + 3/2 = 18/2 = 9 km/hr. - Speed upstream = Speed in still water - Speed of stream = 15/2 - 3/2 = 12/2 = 6 km/hr. - Total time taken for the round trip = 50 minutes = 50/60 hours = 5/6 hours. - Let the distance to the place be 'd' km. - Time taken to row downstream = d / Speed downstream = d/9 hours. - Time taken to row upstream = d / Speed upstream = d/6 hours. - Total time = Time downstream + Time upstream => d/9 + d/6 = 5/6. - Find a common denominator for 9 and 6, which is 18. Multiply the equation by 18: 18(d/9) + 18(d/6) = 18(5/6). - This simplifies to 2d + 3d = 3 5. - 5d = 15. - d = 15/5 = 3 km.
A man can row 7 1/2 km per hour in still water. If in a river running at 1 1/2 km an hour, it takes him 50 minutes to row to a place and back, how far off is the place?
Asked in BPSC Prelims Exam 63rd · Topic: Mechanics (Newton's Laws of Motion and their applications)
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