A man in a boat rowing away from a light house 100m height takes 2 min too change the angle of eleva...........

Quantitative Aptitude ( CCS) Height and Distance

A man in a boat rowing away from a light house 100m height , takes 2 min too change the angle of elevation of top of the light house from 60° to 45° find speed of boat?

.25 m/s

.35 m/s

12.5 m/s

Can't be determined

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Explanation:

Height of the Light house , p = 100 m
let initial distance be x m
and the angle is 60°
so, tan60° = p/x = 100/x
or, √3 = 100/x
or, x = 100/√3 m
Now after time 2min let the new distance be y
and angle is 45°
so, tan45° = 100/y
so, 1 = 100/y
so, y = 100 m
So, distance travelled in 2min
= y - x = 100 - 100/√3 = 100 - 57.737
= 42.263 m
So, d = 42.263 m
t = 2 min = 2×60 = 120 sec
speed = d/t = 42.263/120 m/s
= 0.35219 m/s