Three people pull simultaneously on a stubborn donkey. Jack pulls directly ahead of the donkey with a force of 83.5 N , Jill pulls with 86.1 N in a direction 45° to the left, and Jane pulls in a direction 45° to the right with 175 N . (Since the donkey is involved with such uncoordinated people, who can blame it for being stubborn?) Find the magnitude of the net force the people exert on the donkey.

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