A simple pendulum, consists of an object suspended by a string. The object is assumed to be a particle. The string, with its top end fixed, has negligible mass and does not stretch. In the absence of air friction, the system oscillates by swinging back and forth in a vertical plane. If the string is 2.70 m long and makes an initial angle of 30.5° with the vertical, calculate the speed of the particle at the following positions. (a) at the lowest point in its trajectory (b) when the angle is 15.0° I thought I could use ac = V^2/r.. but I got the wrong answers anyone have any hints for me on what I use for formulas?