# The law of conservation of energy

1. Dec 2, 2011

### cpaquette

I'm doing my physics homework and for one of the questions i have to find m(mass) when i already know Ek(kinetic energy) and v(velocity) with the equation Ek=(1/2)mv^2. I was just wondering if someone could tell me how to move the m in front of the equal sign and to move Ek to the other side.

2. Dec 2, 2011

### Staff: Mentor

It is easier, and just as valid, to keep Ek on the side where it is, and to keep m on the side where it is. Just isolate the m, so it becomes the only variable on the RHS. For example, multiply both sides by 2, and that will get rid of that pesky (1/2) that's alongside the m. Then do something about the v^2 so that it disappears from the RHS.

3. Dec 2, 2011

### cpaquette

Yeah, I gave up on trying to change sides and just added in the variables then divided Ek by 1/2 and v to get m but thanks for helping. I'll remember to multiply by 2 to get rid of the 1/2 next time.

4. Dec 2, 2011

### Staff: Mentor

divided by v^2 I hope?

You could have swapped all on one side with everything on the other side right from the start, before thinking about doing any cancelling, if it was important that m be on the LHS rather than the RHS.