Q4 of 12 Page 203

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.

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


More from this chapter

All 12 →
2

An electric pole casts a shadow of length 20m at a time when a tree 6m high casts a shadow of length 8m. Find the height of the pole.

 3

Two poles 18m and. 13 m high stand upright in a playground. If their feet are 12 m apart find the distance between their top?

 5

An aeroplane at an altitude of 200 m observes the angle of depression of opposite points on the banks of a river to be 45° and 60°. Find in metres the width of the river.

 6

An aircraft is flying at a constant height with a speed of 360 km/hr. From a point on the ground, the angle of elevation at an instant was observed to be 45°. After 20 sec. the angle of elevation was observed to be 30°. Determine the height at which the aircraft is flying (√3 + 1) km or 2.732 km.