Check the uncertainty principle for the wave function in Equation 2.129. Hint: Calculating $\left\langle p^{2}\right.$ ) is tricky, because the derivative of $\psi$ has a step discontinuity at $x=0$. Use the result in Problem 2.24(b). Partial answer:
$\left\langle p^{2}\right\rangle=(m \alpha / \hbar)^{2} .$