Q) The angle of elevation of a jet plane from a point A on the ground is 60°. After a flight of 30 seconds, the angle of elevation changes to 30°. If the jet plane is flying at a constant height of 3600 √3 m, find the speed of the jet plane.

Ans: Let’s start with the diagram for this question:

Step 1: Let’s start from Δ APQ, tan A = tan 60° =

∴  √3 =

∴ S = 3600 m

Step 2: Next, we take Δ ABC, tan A =

∴ tan 30 =

∴

∴ S + D = 3600 √3 x √3 = 10800

∴ D = 10800 – S = 10800 – 3600   [∵ S = 3600 from part (i)]

∴ D = 7200 m

Step 3: Given that the jet plane covered the distance D in 30 seconds

and we calculated D = 7200 m

∴ Speed of the Jet Plane =

= meter /second

= km / hour

= 864 km/hr

Therefore, speed of the jet plane is 864 km/hr

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