Q. 44.1( 18 Votes )

The angle of elevation of a jet fighter from a point A on the ground is 60° . after a flight of 15 seconds the angle of elevation changes to 30° .if the jet is flying at the speed 720 km/h find the constant height at which the jet is flying.

Answer :

The figure is given below:



Let jet fly at a constant height of y km


and let the distance from a point to the starting point of jet bet x km.


Thus, BD = EC = y km


And, AB = x km


As distance = speed × time.


Distance took by jet to travel from D to E =


DE = 3km


Using trigonometry;


DAB = 60°


tan 60° = √3




Also, EAC = 30°









y = 2.59 m


So, the constant height of the jet is 2.59 km


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