Q16 of 22 Page 9

As observed from the top of a light house, 100 m high above sea level, the angles of depression of a ship, sailing directly towards it, changes from 30° to 60°. Find the distance travelled by the ship during the period of observation. (Use √3 = 1.73)(CBSE 2016)


Let AB be the light house, B be the top of light house,


And C and C' be the positions of ship as angle of depression changes from 30° to 60°


We can draw a mathematical diagram for the above problem.


We know that,


In ∆ABC





AC = 173 m


In ∆ABC'





AC' = 57.8 m (appx)


Distance travelled by ship


AC - AC' = 173 - 57.8 = 115.2 m

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