# Combining two equations

1. May 19, 2007

### music_lover12

How do I combine these two equations?

Fc=mv(squared)/r
Fg=qvb

2. May 19, 2007

### cristo

Staff Emeritus
You need to make an effort yourself, and furthermore, defined your symbols. For example, on the LHS of each equation, you have Fc and Fg, respectively. Are these Fxc and Fxg, or are they different variables Fc and Fg?

3. May 19, 2007

### music_lover12

It is with the smaller c and g.

4. May 19, 2007

### cristo

Staff Emeritus
Well, in that case, can you rearrange the second equation to get it into the form v=... ?

5. May 19, 2007

### music_lover12

Yeah, it would be v=f/qB....

6. May 19, 2007

### music_lover12

...also I'm trying to combine the two equations to find m, which is mass.

7. May 19, 2007

### cristo

Staff Emeritus
Ok, so you now have Fc=mv2/r and v=Fg/qB. Now, can you substitute the second equation into the first? [i.e. replace v^2 in the first with Fg/qb]

Right, well if you manage to do the substitution above, then you need to rearrange the equation you obtain to get it in the form m=...

8. May 19, 2007

### music_lover12

Okay, so I substituted the second equation into the first and I got Fc=m*fg/qB/R. Is that right?

9. May 19, 2007

### cristo

Staff Emeritus
No, v is squared in the first equation, and thus substituting the second into the first should yield $$F_c=\frac{m}{r}\left(\frac{F_g}{qB}\right)^2$$. Can you rearrange this?

10. May 19, 2007

### music_lover12

m=Fcr*qB/Fg^2 :uhh:

11. May 19, 2007

### cristo

Staff Emeritus
Well, you're missing a square on q and B; adding parentheses like this m=Fcr*(qB/Fg)^2 gives the correct solution.

12. May 19, 2007

### music_lover12

Oh okay. I see. Thank you very much!

13. May 19, 2007

### cristo

Staff Emeritus
You're welcome.

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