Question: An object at a distance p from a thin glass lens produces an image at a distance q from the lens, where
(1/p) + (1/q) = (1/f)
The constant f is called the focal length of the lens. Suppose an object is moving at 3 mm per second toward a lens of focal length 15 mm. How fast and in what direction is the image moving at the moment at which the object is 35 mm from the lens?