The height of a light house is 85 m. An observer on it found the
angle of depression to a boat to be 30°, which was sailing towards
the light house. After 2 minutes, the angle of depression for the same
boat was 60°. What was the speed of the boat in km/hr ? (V3 = 1.7)
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The speed of the boat is 3 Km/hr.
Step-by-step explanation:
In the figure, tan(30) = AB=1=AB
BD √3 BD
BD = √3 AD
Also tan(60) = AB / BC = √3 = AB / BC
BC= 1/√3 AB
CD = BD = BC= AB( 3 − 1 /√3) = 2AB / √3
= 2 /√3 x 85 = 170 / √3
Speed = Distance / Time = 170 / √3 x 60 2 x 10
= 3 Km/hr
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