Q39 of 40 Page 1

The angle of elevation of an airplane from a point on the ground is 60⁰. After a flight of 30 seconds, the angle of elevation becomes 30⁰. If the airplane is flying at a constant height of 3000√3 m, find the speed of the airplane.

200 m/s



Let, initially plane is at C and after 30 seconds it moves to D. therefore, distance travelled by plane in 30 secs = CD = AE = y m


Let, AB = x m


Height of plane from ground = AC = DE = 3000√3 m


In ∆ABC,




∴ x = 3000 m


Now, in ∆ADE,





∴ 3000 + y = 3000√3 × √3


∴ 3000 + y = 9000


∴ y = 6000 m


Therefore, distance travelled by plane in 30 secs is 6000 m


Therefore, speed of plane is




∴ speed = 200 m/s


Hence, speed of the airplane is 200 m/s.


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