Question

A man in a boat rowing away from a lighthouse 100m high takes 2 minutes to change angle of elevation of the top of a lighthouse from 60 degree to 45degree find the speed​

Answer 1

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Consider ΔABC

Where AB is Height of Tower 

BC is distance from boat to tower

tanC = AB/BC

⟹√3 = 100/BC

⟹BC = 57.73

Now let D be the point the boat travelled 

tanD = AB/BD

⟹√31 = 100/BD

⟹BD = 173.2

 

Distance travelled by boat CD

=BD − BC

=173.2 − 57.73

=115.47m

Speed of boat

= 115.47/2

= 57.73 m/min