# Which GPE formula is right and when do I use this other

1. Oct 30, 2015

### zachdr1

In my formula sheet I have written down that

deltaPEg = (PEg final - PEg initial)

but then I have written down that

-(deltaPEg) = (PEg final - PEg initial)

which one is right?

Oh and another question, when do I use the formula

deltaK + deltaPE = 0?

2. Oct 30, 2015

### Staff: Mentor

Depends on the sign convention you like for the energy difference.

When it is applicable and helps.

Physics is not about memorizing formulas, it is about understanding how to get the formulas needed to solve the problem.

3. Oct 30, 2015

### Staff: Mentor

While I agree with mfb, I do think that the convention for the $\Delta$ symbol is pretty standard. I would always use $\Delta f = f_{final}-f_{initial}$ for any and all $f$.

4. Nov 1, 2015

### Mister T

When the total mechanical energy of a system is constant (conserved).