Solution (source code)

= Solution

For longitudinal motion in transverse subband $i$,
$$
\boxed{\epsilon_i(k)=E_i+\frac{\hbar^2k^2}{2m},\qquad v(k)=\frac1\hbar\frac{d\epsilon_i}{dk}=\frac{\hbar k}{m}.}
$$
For a completely <free particle> take $E_i=0$ and use the full <wave vector>. In a <semiconductor> the parabolic-band <mass> is the appropriate <effective mass> rather than necessarily the bare <electron> <mass>.