A launch travels across a river from point A to point B on the opposite bank along a straight line AB forming an angle α with the bank. The wind blows with a velocity of u at right angles to the bank. The flag on mast of the launch forms an angle β with the direction of its motion : (Given α = 60º, β = 60º)
(i) Speed of the launch with respect to wind is–
Text Solution
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Ans.
(i)
Sol . u tan 30º
(ii)
Sol. Data is insufficient
(iii)
Sol.
u 0 = velocity of wind relative to launch
v = speed of launch with respect to the bank
∠ DCF + ∠ FCB = β
∠ DCF + 
– α = β
∠ DCF = α + β – 
∠ FDC = π – β
= 
Time taken by the launch to cross the river is
t = 
= 
/ 
tan 30º = 80 
s
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