A Boat is being rowed away in still water, from a 210 metres high cliff at the speed of 3 km/hr. What is the approximate time taken for the angle of depression of the cliff at the boat to change from 60 deg. To 45 deg.? ?->(Show Answer!)

1. A Boat is being rowed away in still water, from a 210 metres high cliff at the speed of 3 km/hr. What is the approximate time taken for the angle of depression of the cliff at the boat to change from 60 deg. To 45 deg.?

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By: anil on 05 May 2019 02.39 am

The distance of boat from bottom of cliff when angle of depression is 60 deg is tan $$60^{circ}$$ = $$frac{210}{d}$$ d = 121.3 m The distance of boat from bottom of cliff when angle of depression is 45 deg is tan $$45^{circ}$$ = $$frac{210}{d}$$ d = 210 m The distance covered by boat is 210 - 121.3 = 98.7 m Speed of boat given is 3 km/hr In m/s it is 3*5/18 = 5/6 m/s = 0.83 m/s Time taken to cover 98.7 m is 98.7/0.83 = 118.9 sec $$cong$$ 2 min

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