Question

The angle of elevation of an airplane from a point A on the ground is 60° after a flight of 30 seconds, the angle of elevation changes to 30°. If the plane is flying at a constant height of 3600 √3 m, find the speed, in km/hour, of the plane.

Answer 1

Let us suppose that DE = x and CD = y

Now, In right ΔBED, we have

⇒ CE = 10800

⇒ CD + DE = 10800

⇒ y + x = 10800

⇒ y + 3600 = 10800

⇒ y = 10800 – 3600

⇒ y = 7200

∵ AB = CD = 7200

We know that,

Hence, the speed of the aeroplane is 864 km/hr