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A moving boat is observed from the top of a 150 m high cliff moving
away from the cliff. The angle of depression of the boat changes from
60° to 45° in 2 minutes. Find the speed of the boat in m/ℎ.
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Answer:
1905 km/hr
Step-by-step explanation:
From figure:
Given, AB = 150 m, ∠ACB = 60°, ∠ACB = 45°.
(i)
cot 45° = AD/AB
⇒ 1 = AD/150
⇒ AD = 150 m.
(ii)
cot 60° = AC/AB
⇒ 1/√3 = AC/150
⇒ AC = 150/√3
= 150/√3 * (√3/√3)
= 150√3/3
= 50√3
= 86.5 m
Now,
CD = AD - AC
= (150 - 86.5)
= 63.5 m
Given that it takes 2 minutes = (2/60) hours = (1/30) hours.
∴ Speed of the boat = (63.5/1/30) m/hr
= (63.5 * 30) m/hr
= 1905 km/hr.
Hope it helps!
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adithganiga:
thanks broi...
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