An aeroplane flying horizontally at a height of 2500m above the ground is observed at a certain point on earth to subtend and angle of 60 0 . After 15 seconds, its angle of elevation at the same point is observed to be 30 0 . Calculate the speed of the aeroplane.
In ∆ABC,
In ∆AED,
From figure,
BD = CE
and, CE = AE - AC
so, BD = AE - AC
now, substitute value of AE and AC from equation (1) and (2), we get,
BD is covered by aeroplane in 15 seconds. So,
Hence, speed of the aeroplane is 192.455 m/s