# Modern Physics Question

1. Feb 10, 2008

### digital19

1. The problem statement, all variables and given/known data

Show that $$d(\gamma mu)=m(1- \frac{u^2}{c^2})^{-3/2} du$$

2. Relevant equations

It is known that is
$$\gamma=\frac{1}{\sqrt{{1- \frac{u^2}{c^2}}}}$$

3. The attempt at a solution

The question stated in part 1 is the precise question given in the textbook.

I'm not sure how to proceed here. I believe it's asking you to take the derivative using the product rule. I even wondered if it was a type and du was supposed to be on the left hand side.

2. Feb 10, 2008

### CompuChip

It's not a typo,
$$d(\gamma mu)=m(1- \frac{u^2}{c^2})^{-3/2} du$$
is just physicists' notation for
$$\frac{d}{du} (\gamma mu)=m(1- \frac{u^2}{c^2})^{-3/2}$$
(if you want, consider du as an infinitesimal quantity, dividing by it gives you a differential quotient aka derivative on the left hand side).
So indeed, you just plug in the expression for $\gamma$ you gave and differentiate w.r.t. u; then simplify to get the requested result

3. Feb 10, 2008

### pam

What text are you using?
$$u^2$$ stands for $$\vec u}\cdot{\vec u}$$.