why devide

HW 2.4 answer key cl A ball of mass m is attached to a vertical rod by two massless strings. The rod is rotated about its axis so that both strings are taut, with tensions 7) and 7, respectively. The strings and rod form the nght triangle shown in the figure above. The ball rotates in a horizontal circle of radius r with speed v. 11. What is the tension 7) in the upper string? (A) mg cos @ (B) mg sin @ (C) mg tan (E) mg/sin @