\[m\ddot{x}=ma\cdot f(x)\]
\[\int \frac{d\dot{x}}{dt}dx=a\int \cdot f(x)dx\]
\[\int \frac{d\dot{x}}{dt}\cdot\frac{dx}{dt}\cdot\frac{dt}{dx}dx=a\int \cdot f(x)dx\]\[\int \dot{x}d\dot{x}=a\int \cdot f(x)dx\]
\[\frac12\dot{x}^2=a(f(x)-f(0))\]
\[|\dot{x}|=\sqrt{2a(f(x)-f(0))}\]