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a man crosses a river in a Boat. if he crosses the river in minimum time he takes 10 min with the drift of 120 m . if he crosses the river taking the shortest path ,he takes 12.5 min then find width of the river |
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Answer» Explanation: Width = d Man = V River = v In minimum time, he goes perpendicular to the river. d/V = 10 min------(1) v x 10 min = 120 m, so v = 12 m /min In minimum distance, the resultant of the velocities is perpendicular to river If he is at ANGLE x with the perpendicular V sinx = v = 12-----(2) V COSX = d / 12.5-----(3) SQUARING and adding (2) and (3) 2V^2 = 144 + d^2 / 156.25 -----(4) Putting VALUE of V from (1) in (4), d^2 /50 = 144 + d^2 /156.25 d^2 = 10500 m d = 100m There could be some calculation error, but the method is correct. |
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