Let the Plane travel a distance x, at any point of time t , starting from the position directly overhead the object, 1 km down on the earth. Also let the angle made by the line of sight with the direction of the plane be θ at this time, as shown in the figure below. It is required to find the rate of change of angle dθ /dt when θ = π/6. Rate of change of x, dx/dt is constant and = 10/36 km/s.

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