the angle of elevation of an aeroplane from a point on the ground is 45 degree. After 15 seconds of flight the angle changes to 30 degree.f the plane is flying at a constant height of 2500m,find the speed of the plane.

Let the initial and final position of the plane be A and B.

Let O be the point of observation.

AA´ and BB´ denote the height of the plane from the ground.

∴ AA´ = BB´ = 2500 m

From ∆OAA´

From ∆OBB´

Distance covered by the plane from A to B is AB or A´B´

⇒ A´B´ = OB´ – OA´

Time taken by the plane in moving from A to B = 15 seconds

Speed of the plane

 

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