How much work is done by the motor in a cd player to make a cd spin, starting from rest? the cd has a diameter of 12.70 cm and a mass of 16.30 g. the laser scans at a constant tangential velocity of 1.150 m/s. assume that the music is first detected at a radius of 20.90 mm from the center of the disk. ignore the small circular hole at the cd's center.

Large electric fields in cell membranes cause ions to move through the cell wall. the field strength in a typical membrane is 1.0 x 10 7 n/c. what is the magnitude of the force on a calcium ion with charge +e? what is its acceleration? is it possible for a particle with the same charge as as calcium to have a different acceleration if placed at this location? what would change the acceleration: mass of the particle? diameter of the particle?