An aeroplane flying horizontally 1000m above the ground is observed at an angle of elevation 60^{0} froma point on the ground.Aftera flight of 10secondsthe angle of elevation at a point of observation changes to 30^{0} .Find the speed of the plane in m/s.

Let us observe the following figure.

Let A and B be the two positions of the aeroplane and let O be the point of observation.

and AC = BD = 1000 m

From the right triangle OCA, we have

From the right triangle ODB, we have

We need to find the speed of the plane.

Thus the speed of the plane is 115.47 m /s

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