Amassless rigid rod, 50 cm long, carris a litle ball of mass 2 kg at one end. at the other a motor makes it rotate in a vertical plane at 30 rev/min. when the ball is at the bottom of its circular trajectory, what is the magnitude of the tension in the rod? (a) 10 n (b)20 n (c)30 n (d)40 n (e)50 n