You are riding in an elevator on the way to the eighteenth floor of your dormitory. the elevator's upward acceleration is a = 1.94 m/s2 . beside you is the box containing your new computer; box and contents have a total mass of 28.4 kg . while the elevator is accelerating upward, you push horizontally on the box to slide it at constant speed toward the elevator door. if the coefficient of kinetic friction between the box and elevator floor is μk = 0.35, what magnitude of force must you apply?

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.)