A man rowing a boat away from a lighthouse which is 100 m high takes 2 min to change the angle of elevation of the light house from 45∘ to 30∘. The speed of the boat is [Tan 45∘=1, Tan 30∘ = 0.57]
37.7 m /min
Let the lighthouse AB=100 m and boat moves from C to D
In △ABCTan 45∘=100CB=1 ⇒ CB=100 m
In △ADBTan 30∘=100DB=0.57 ⇒DB=1000.57=175.4 mCD=BD−BCCD=175.4−100=75.4It takes 2 min to move from C to DSpeed=DistanceTime=75.42=37.7m/min