# Calculate the speed of the particle

1. Dec 3, 2007

### mkwok

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?

2. Dec 3, 2007

### hage567

Try conservation of energy (gravitational potential energy and kinetic energy). Take the bottom position as your reference point.

3. Dec 4, 2007

### wysard

In free space, umm it doesn't.

You have a hypothetical string of no mass in with a hypothetical end point. Are we to assume it is in a hypothetical Earth gravity or some other space?