A moving boat is observed from the top of a 150 m high cliff mov

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 Multiple Choice QuestionsShort Answer Type

171.

A man standing on the deck of a ship, which is 10 m above water level, observes the angle of elevation of the top of a hill as 60° and the angle of depression of the base of a hill as 30°. Find the distance of the hill from the ship and the height of the hill.

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172.

The angle of elevation of the top Q of a vertical tower PQ from a point X on the ground is 60o. From a point Y, 40 m vertically above X, the angle of elevation of the top Q of the tower is 45o. Find the height of the tower PQ and the distance PX. Use square root of 3 space equals 1.73

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173.

In Given figure, a tower AB is 20 m high and BC, its shadow on the ground, is m20 square root of 3 long. Find the sun's altitude.

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174. The angle of elevation of an aeroplane from a point A on the ground 60°. After a flight of 15 seconds, the angle of elevation changes to 30°. If the aeroplane is flying at a constant height of 1500 space square root of 3 space end root space straight m, find the speed of the plane in km/hr.

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 Multiple Choice QuestionsLong Answer Type

175. At a point A, 20 metres above the level of water in a lake, the angle of elevation of a cloud is 30°. The angle of depression of the reflection of the cloud in the lake, at A is 60°. Find the distance of the cloud from A.
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 Multiple Choice QuestionsShort Answer Type

176.

The ratio of the height of a tower and the length of its shadow on the ground is √3:1. What is the angle of elevation of the sun?

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177.

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.


Let the distance BC be x m and CD be y m. 



In ∆ABC,
tan space 60 degree space equals space AB over BC space equals space 150 over straight x
rightwards double arrow space square root of 3 space equals space 150 over straight x
rightwards double arrow space straight x space equals space fraction numerator 150 space straight m over denominator square root of 3 end fraction.... space left parenthesis straight i right parenthesis

In ABD,
tan space 45 degree space equals space AB over BD space equals space fraction numerator 150 over denominator straight x plus straight y end fraction
rightwards double arrow space 1 space equals space fraction numerator 150 over denominator straight x plus straight y end fraction
rightwards double arrow straight x space plus straight y space equals space 150
rightwards double arrow space straight y space equals space 150 minus straight x

Using (1), we get
rightwards double arrow space straight y space equals space 150 space minus fraction numerator 150 over denominator square root of 3 end fraction space equals space fraction numerator 150 left parenthesis square root of 3 minus 1 right parenthesis over denominator square root of 3 end fraction space straight m
Time taken to move from point C to point D is 2 min = 2/60 h=1/30 h.
Now,
Speed space equals space Distance over Time space equals space fraction numerator straight y over denominator 1 divided by 30 end fraction
space equals space fraction numerator begin display style fraction numerator 150 left parenthesis square root of 3 minus 1 right parenthesis end root over denominator square root of 3 end fraction end style over denominator 1 divided by 30 end fraction space equals space 1500 square root of 3 left parenthesis square root of 3 minus 1 right parenthesis straight m divided by straight h
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 Multiple Choice QuestionsLong Answer Type

178.

The angle of elevation of a cloud from a point 60 m above the surface of the water of a lake is 30° and the angle of depression of its shadow in water of lake is 60°. Find the height of the cloud from the surface of the water. 

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 Multiple Choice QuestionsShort Answer Type

179.

As observed from the top of a 100 m high light house from the sea-level, the angles of depression of two ships are 30° and 45°. If one ship is exactly behind the other on the same side of the light house, find the distance between the two ships. [ Use √3= 1.732 ]


 Multiple Choice QuestionsMultiple Choice Questions

180.

The angle of depression of a car, standing on the ground, from the top of a 75 m high tower, is 30o. The distance of the car from the base of the tower (in m.) is

  • 25√3

  • 50√3

  • 75√3

  • 150


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