A small ball swings in a horizontal circle at the end of a cord of length l1, which forms an angle θ1 with the vertical. The cord is then slowly drawn through the support at O until the length of the free end is l2. (a) Derive a relation among l1, l2, θ1, and θ2. (b) If the ball is set in motion so that initially l1 5 0.8 m and θ1 5 35°, determine the angle θ2 when l2 5 0.6 m.

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?