The second derivative is given by:
\[
f''(x) = 100x^2 e^{-5x^2} - 10 e^{-5x^2}
\]
The \( x \)-values where \( f''(x) = 0 \) are:
\[
x = -\frac{\sqrt{10}}{10}, \frac{\sqrt{10}}{10}
\]
Thus, the final answers are:
\[
\boxed{f''(x) = 100x^2 e^{-5x^2} - 10 e^{-5x^2}}
\]
\[
\boxed{x = -\frac{\sqrt{10}}{10}, \frac{\sqrt{10}}{10}}
\]