A boat which can move with a speed of 5 m/s relative to water crosses a river of width 480 m flowing
with a constant speed of 4 m/s. What is the time taken by the boat to cross the river along the shortest
path.
(A) 80 s
(B) 160 s
(C) 240 s
(D) 320 s
Answers
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9
Answer:
160 secs
Explanation:
A boat which can move with a speed of 5 m/s relative to water crosses a river of width 480 m flowing with a constant speed of 4 m/s. What is the time taken by the boat to cross the river along the shortest path.
5 Cosα is horizontal speed
& 5 sinα is Vertical speed
to go from shortest path
5Cosα cancels 4 m/s
=> Cosα = 4/5
=> Sinα = √( 1 -Cos²α) = √( 1 - (4/5)²) = 3/5
5Sinα = 5 * 3/5 = 3 m/s
Width = 480 m
Distance = 480 m
Speed = 3m/s
Time = 480/3 = 160 secs
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