# Homework Help: How to simplify

1. Dec 10, 2005

### LENIN

I have to find out how to make this simplification
$$2\pi \sqrt{ \frac {Ml^2+2Mr^2/5+m(l-r)^2/3} {(Ml+m(l-r)/2)g}} \approx 2\pi \sqrt{\frac{l}{g}(1+\frac{2r}{5l}-\frac{1m}{6M})}$$.:surprised :surprised

This is for a project I have to do, but I have never done any such simplifications before. I don't know which parts of the equation are important and which aren't. If it helps this are the values of the variables:

$$M\approx10kg$$
$$m\approx20g$$
$$l=227cm$$
$$r=6cm$$

2. Dec 10, 2005

### Astronuc

Staff Emeritus
$$(Ml+m(l-r)/2)g$$ would simplify to ~Mlg, in the denominator under the root.

(l-r)2 would simplify to l2 for very small r, otherwise l2-2rl since r2 would be small.

r/l = 6/227 = 0.026

m/M = 0.02/10 = 0.002 so M-m ~ M is a good approximation.

3. Dec 12, 2005

Thank you.