A man wishes to cross a river in a boat. If he crosses the river in minimum time he takes 10 minutes with a drift of 120 m. If he crosses the river taking shortest route, hetakes 12.5 minutes, find velocity of the boat with respect to water.
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a
20 m/min
b
12 m/min
c
10 m/min
d
8 m/min
answer is A.
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Detailed Solution
10=Lv ......(1)12.5=Lv2−u2=Lv1−u2/v2 ..(2)from (i) and (ii) 1012.5=Lv×v1−u2/v2L45=1−122v21625=1−122v2⇒122v2=1−1625=92512v=35⇒v=12×53=20m/min
A man wishes to cross a river in a boat. If he crosses the river in minimum time he takes 10 minutes with a drift of 120 m. If he crosses the river taking shortest route, hetakes 12.5 minutes, find velocity of the boat with respect to water.