# Homework Help: Help needed with rearranging an equation

1. Nov 20, 2011

### Hussman

Im having trouble rearranging an equation to find a value for I.

[The given equation is mgh = 1/2*Iw^2 + 1/2*mv^2 + Tf * theta

My attempt was a bit of a stab in the dark as i am useless with rearranging equations.

I = mgh/w^2 + 1/2*mv^2 + Tf * theta

Many thanks

2. Nov 20, 2011

### grzz

To make I subject of the equation is like peeling an onion.

First step: Transfer those two terms on the RHS not involving I to the LHS.

3. Nov 20, 2011

### Hussman

ok so you end up with

mgh - 1/2*mv^2 - Tf*theta = 1/2*Iw^2

Would the lhs be divided by 1/2 w^2?

Thanks

Last edited: Nov 20, 2011
4. Nov 20, 2011

### grzz

Yes we 'peel the next layer of the onion' by dividing BOTH sides by $\frac{\omega^{2}}{2}$ to isolate the I by itself on the RHS.

5. Nov 23, 2011

### Hussman

Nice one cheers