# Simple (supposedly) pendulum with unknown length and kinetic energy

1. Nov 30, 2004

### VinnyCee

Please help, if a 60 g bob at the end of a cord (unknown length) of negligable mass and the angle $$\Theta = (0.0800 radian) cos[(4.43 radian / s.) t + \phi]$$ <---- Angle between cord and the vertical.

What are
a) the pendulum's length?

b) it's maximum kinetic energy?

Please help, the prof did not go over any of this type of problem.

2. Nov 30, 2004

### Tide

The 4.3 rad/s is the angular frequency which is related to the length of the pendulum. Can you take it from there?

3. Nov 30, 2004

### Justin Lazear

Google is a wonderful thing.

http://hyperphysics.phy-astr.gsu.edu/hbase/pend.html

If you don't understand about pendulums, I'd suggest learning about the system before throwing numbers at equations.

--J

4. Nov 30, 2004

### VinnyCee

Ok, I gto part a) but not part b). Please help

a) 0.494 meters

But how do I relate that to find the x_max?

5. Nov 30, 2004

### HallsofIvy

Staff Emeritus
The kinetic energy will be highest when speed is highest. At what point is the speed of the pendulum highest? (If by x_max, you mean the highest point the pendulum reaches, that is irrelevant.)