As you work with a block and tackle, you seem to be working hard, so you decided to investigate. You know that a force of 2000 N is needed to lift the object. You measure your exerting force of 400 N as you pull the rope down 6 m to lift the weight a distance of 1 m. What is the efficiency of the block and tackle?

With the simplified model of the eye, what corrective lens (specified by focal length as measured in air) would be needed to enable a person underwater to focus an infinitely distant object? (be careful-the focal length of a lens underwater is not the same as in air! assume that the corrective lens has a refractive index of 1.62 and that the lens is used in eyeglasses, not goggles, so there is water on both sides of the lens. assume that the eyeglasses are 1.90