# Simple algebra to find the strict mass–energy equivalence formula, and I cant do it

1. Dec 29, 2012

### cobi18

Simple algebra to find the strict mass–energy equivalence formula, and I cant do it!!

find ((m^2)*(c^4)=(E^2)-(p^2*c^2)) from (E=m*c^2*y) (p=m*y*v)
(y=1/(1-(v^2/c^2))^(1/2))

Yeh i can find the m^2c^4 parts and the E^2 obvioulsy. but then i am stuck with E^2(v^2/c^2) when instead i want (p^2c^2). If anyone could help that would be great!

2. Dec 29, 2012

### Staff: Mentor

Re: Simple algebra to find the strict mass–energy equivalence formula, and I cant do

Use E=m*c^2*y again.

3. Dec 30, 2012

### cosmic dust

Re: Simple algebra to find the strict mass–energy equivalence formula, and I cant do

That will not solve anything... The formula for the momentum has to be used. I recommend you to start with "p = γmv" and find "v" as a function of "p", then find "γ" as a function of "p" and finaly replace "γ" in "E=γmc2" with what you have found.

4. Dec 30, 2012

### Staff: Mentor

Re: Simple algebra to find the strict mass–energy equivalence formula, and I cant do

Sure it will. It's the first step:
-step 1: use the formula for E as I described
Of course it does. That's the second step:
-step 2: then rewrite the results in terms of p

5. Dec 30, 2012

### cosmic dust

Re: Simple algebra to find the strict mass–energy equivalence formula, and I cant do

OK, I thought you had say to use the formula for E twice, sorry...