Q14 of 47 Page 1

The angle of elevation of an aeroplane from a point on the ground is 60°. After a flight of 30 seconds, the angle of elevation becomes 30°. If the aeroplane is flying at a constant height of 3000√3 m, find the speed of the aeroplane.


Let C and E be the initial and final position of the aeroplane


According to the figure,


tan 30° =


⇒


⸫ AD = 3000 × 3 = 9000 m


tan 60° =


⇒


⸫ AB = 3000 m


⸫


Distance travelled in 30 seconds by the aeroplane = BD = 9000 – 3000 = 6000 m


Time given = 30 seconds


Speed = = 200 m/s


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