# CBSE Class 10-Mathematics: Chapter –9 Some Applications of Trigonometry Part 10

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**Question 16:**

An aeroplane flying horizontally at a height of above the ground is observed at a certain point on the earth to subtend an angle of After seconds, its angle of elevation is observed to be . Calculate the speed of aeroplane in .

**Answer:**

Let be the observation point.

Let A be the position of aeroplane such that

Let B be the position of aeroplane after seconds.

In right

In right

Eq.(ii)

Distance covered in 15 seconds

Distance covered in seconds

**Question 17:**

A man is standing on the deck of a ship which is above water level. He observes the angle of elevation of the top of a lighthouse as and the angle of depression of the base of the lighthouse as .Calculate the height of the lighthouse.

**Answer:**

Height of lighthouse

In right

In right

In right

Now