# A Navy captain going away from a lighthouse at the speed of m/s. He ob

| A Navy captain going away from a lighthouse at the speed of m/s. He observes that it takes him 1 minute to change the angle of elevation of the top of the lighthouse from 60

^{o}to 45^{o}. What is the height (in metres) of the lighthouse?A. 240√3

B. 480[(√3) – 1]

C. 360√3

D. 280√2

### Right Answer is: A

#### SOLUTION

Let the height of light box be h.

Let BC = 1 unit

In triangle ABC

unit

In Δ ABD,

unit

Then CD = ( – 1 ) unit

Here CD is the distance which he travels in 60 seconds at the speed of 4( – 1 ) m/s

A.T.Q.

( – 1) unit = 4( – 1)*60

1 unit = 240

Then

AB = × 240

AB = 240 .

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