A 60-g steel sphere attached to a 200-mm cord can swing about point O in a vertical plane. It is subjected to its own weight and to a force F exerted by a small magnet embedded in the ground.The magnitude of that force expressed in newtons is F= 3000/r2 , where r is the distance from the magnet to the sphere expressed in millimeters. Knowing that the sphere is released from rest at A , determine its speed as it passes through point B.
