Hello! I need some help with this problem, please!

Let $\displaystyle f$ be a field and $\displaystyle \gamma$ a curve such that for all $\displaystyle t\in{\mathbb{R}}$ happens that $\displaystyle f(\gamma (t))=m\gamma ''(t)$ (where m is a constant).

Show that:

$\displaystyle \displaystyle\int_{\gamma (a)}^{\gamma (b)}fd\gamma = \displaystyle\frac{1}{2}m \left\|{\gamma ''(b)}\right\|-\displaystyle\frac{1}{2}m \left\|{\gamma ''(a)}\right\|$

Thank you!!