Aceiling fan consists of five blades of 0.80 m length and 0.10 m width, which rotate at 100 rpm. estimate the torque needed to overcome the friction on the blades if they act as flat plates. (hint: at each location r along the length of the plate, the approach velocity will be 2πn×y where 0 < y < l and l is the blade length (0.8 m) and n is the rotational speed (rpm).

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