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.