Question

A policeman is standing near a highway using a radar gun to catch speeders. He aims the gun at a car that has just passed his position and, when the gun is pointing at an angle of 45(degrees) to the direction of the highway, notes that the distance between the car and the gun is increasing at a rate of 100km/h. How fast is the car travelling?
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Answer 1

The speed obtained is the y-component of the actual speed of the car. The y-component and actual speed are related by:
Vy = Vsin(∅)
100 = Vsin(45)
V = 141.4 km/h