The hammer throw is a track-and-field event in which a 7.30-kg ball (the hammer) is whirled around in a circle several times and released. it then moves upward on the familiar curved path of projectile motion and eventually returns to the ground some distance away. the world record for the horizontal distance is 86.75 m, achieved in 1986 by yuriy sedykh. ignore air resistance and the fact that the ball was released above the ground rather than at ground level. furthermore, assume that the ball is whirled around a circle that has a radius of 1.68 m and that its velocity at the instant of release is directed 33.9 ° above the horizontal. find the magnitude of the centripetal force acting on the ball just prior to the moment of release.

People with normal vision cannot focus their eyes underwater if they aren't wearing a face mask or goggles and there is water in contact with their eyes. in a simplified model of the human eye, the aqueous and vitreous humors and the lens all have a refractive index of 1.40, and all the refraction occurs at the cornea, whose vertex is 2.60 cm from the retina. 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 2.05cm in front of the eye.)