Question

A person is watching a boat from the top of a lighthouse. The boat is approaching the lighthouse directly. When first noticed, the angle of depression to the boat is 16°23'. When the boat stops, the angle of depression is 49°29' . The lighthouse is 200 feet tall. How far did the boat travel from when it was first noticed until it stopped? Round your answer to the hundredths place.

Answer 1

509.35 feet

Explanation:

16°23' means 16 degrees and 23 minutes. A minute is 1/60 of a degree.

16°23' = 16 + (23/60) = 16.383°

Similarly:

49°29' = 49 + (29/60) = 49.483°

When the boat is first noticed:

tan(16.383°) = 200 / a

a = 200 / tan(16.383°)

a = 680.27

When the boat stops:

tan(49.483°) = 200 / b

b = 200 / tan(49.483°)

b = 170.92

So the difference is:

a − b = 680.27 − 170.92 = 509.35

The boat traveled 509.35 feet from the time it was first noticed to the time it stopped.