A boat which has a speed of 5ms−1 in still water crosses the river of width 25m in 10 seconds. The boat is heading at an angle of α with downstream, where α is equal to
A
150∘
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B
120∘
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C
90∘
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D
60∘
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Solution
The correct option is A150∘ We know that the time taken for the boat to cross the river is given by,
t=wvsinθ
Given w=25m is the width of the river, time to cross river is t=10s and velocity of boat is v=5ms−1
⇒10=255sinθ
⇒sinθ=12
⇒θ=30∘ ∴α=180∘−θ=150∘ ∴ The correct answer is option A