Q.

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 hill as 30 °  . Find the distance of the hill from the ship and the height of the hill.


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a

The distance of the hill from the ship is 3   m and the height of the hill is 40 m

b

The distance of the hill from the ship is 10 3   m and the height of the hill is 40 m

c

The distance of the hill from the ship is 2 3   m and the height of the hill is 60 m

d

The distance of the hill from the ship is 10 3   m and the height of the hill is 10 m 

answer is B.

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Detailed Solution

Given that a man is standing on the deck of a ship, which is 10 m above the water level, observes the angle of elevation of the top of a hill as 60 0   and the angle of depression of the base of hill as 30 0   .
We need to find the distance of hill from the ship and the height of the hill.
Question ImageFrom the corresponding figure, let us assume that the point of observation is at A and the height of the deck is 10 m.
 Thus, AB=CD=10m   Therefore, the angle of elevation of the top of hill is EAD= 60 0   The angle of the depression of the base of hill is DAC= 30 0  .
Let us assume that, in triangle ΔADE  , AD=BC=x m  
From the figure ΔADE  ,
tanθ= opposite side adjacent side  
  tan 60 0 = ED DA  . Use the value of trigonometric angle tan 60 ° = 3   .
3 = h x h= 3 x.....(1)  
Consider the triangle ΔABC   ,
tanθ= opposite side adjacent side  
Thus, tan 30 0 = AB BC   Use the value of the trigonometric angle tan 30 ° = 1 3  
1 3 = 10 x x=10 3 .(2)   The distance of the hill from the ship is x=10 3  .
Substitute the value of x from equation (2) in equation (1),
h=(10 3 ) 3 h=10×3 h=30.(3)  
The height of the hill is CE, i.e.,
CE=CD+DE CE=10+h.(4)   Substitute the value of h from equation (3) in equation (4).
CE=h+10 CE=30+10 CE=40 m  
The height of the hill is 40 m.
Thus, the distance of the hill from the ship is 10 3  m and the height of the hill is 40 m.
Therefore, the correct option is 2.
 
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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 hill as 30 °  . Find the distance of the hill from the ship and the height of the hill.