posted by laur on .
You've dropped a lucky penny into the middle of a hemispherical water basin of radius 3m. There is a light on the upper edge of the basin. The penny falls vertically along the axis of symmetry of the basin, and when it is 1m from the bottom of the basin it is falling at 2m/s. How fast is the shadow of the penny moving along the surface of the basin at this instant?