Draw the necessary diagram for this question.
A man on the top of a lighthouse observes the angle of depression of two ships on the opposite sides of the lighthouse as 32° and 58° respectively. If the height of the lighthouse is 120 m, find the distance between the two ships. Give your answer correct to the nearest meter.
Show SolutionHide Solution↓
Let AD be the lighthouse and B and C be the two ships on the opposite sides of the lighthouse.
Given,
Height of the lighthouse (AD) = 120 m
The angles of depression of the two ships are 32° and 58°.
From figure,
⇒ ∠FAB = ∠ABD = 32° (alternate angles are equal)
⇒ ∠EAC = ∠ACD = 58° (alternate angles are equal)
In right angled triangle ABD,
$$\begin{aligned}\Rightarrow \tan 32° = \frac{\text{Perpendicular}}{\text{Base}} \\[1em] \Rightarrow \tan 32° = \frac{AD}{BD} \\[1em] \Rightarrow BD = \frac{AD}{\tan 32°} \\[1em] \Rightarrow BD = \frac{120}{0.6249} \\[1em] \Rightarrow BD = 192.03 \text{ m}.\end{aligned}$$
In right angled triangle ACD,
$$\begin{aligned}\Rightarrow \tan 58° = \frac{\text{Perpendicular}}{\text{Base}} \\[1em] \Rightarrow \tan 58° = \frac{AD}{CD} \\[1em] \Rightarrow CD = \frac{AD}{\tan 58°} \\[1em] \Rightarrow CD = \frac{120}{1.6003} \\[1em] \Rightarrow CD = 74.99 \text{ m}.\end{aligned}$$
From the figure,
Distance between the two ships (BC) = BD + CD
= 192.03 + 74.99
= 267.02 m ≈ 267 m.
Hence, the distance between the two ships = 267 m.