Calculating first and second derivative the following

Question

$u(x)=\dfrac{1}{(\phi'(x))^l}v(t)$

where $t=\phi(x)$.

I calculate the first derivative as follows

$\dfrac{du}{dx}=((\phi'(x))^{-l})'v(t)+(\phi'(x))^{1-l}\dfrac{dv(t)}{dt}$

Is it right? And

$\dfrac{d^2u}{dx^2}=?$