Question

the angle of elevation of a jet plane from point A on the ground is 60°after a flight of 15 second.The Angle of elevation changes to 30° if the plane is flying at a constant height of 1500√3 metre find the speed of the jet plane​

Answer 1

.

Let A be the point of observation on the ground and B and C be the two positions of the jet. Let BL=CM = h metres. Let AL = x metres.

Speed of the jet = 720 km/hr =720 m/sec = 200 m/sec

Time taken to cover the distance BC is 15 sec.

Distance BC = LM = 200 15 m = 3000 m

In ALB,

cot 60° =

=

x= ……………….. (i)

In AMC,

cot 30° =

x+3000 = h

x= h -3000 ………………(ii)

From (i) and (ii)

h-3000 =

3h-3000 = h

2h= 5196

h=2598

Thus, the height at which the jet is flying is 2598 m.