Let's begin with the angular acceleration of a compact disk (cd). to play music the cd must rotate at high speed while a laser reads data encoded in a spiral pattern on the disk. the disc has radius r=6.0cm=0.060m; when data are being read, it spins at 7200 rev/min. what is the cd's angular velocity ω in radians per second? how much time is required for it to rotate through 90∘? if it starts from rest and reaches full speed in 4.0 s, what is its average angular acceleration?

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.)

Whithin which type of system is neither the total mass nor the total energy conserved ? a. open b. connected c. isolated d. closed

What is the change in internal energy if 20 j of heat is released from a system and the system does 50 j of work on the surroundings? a. -70 j b. 30 j c. -30 j d. 70 j