Answer
In a finite well, the magnitude of the momentum is less than it would be if the potential well were infinite.
Work Step by Step
In a finite well, the matter wave leaks into the walls of the well. However, in an infinite well, the matter wave is restricted by the walls of the well.
Therefore, in a finite well, the de Broglie wavelength $\lambda$ is greater than it would be if the potential well were infinite.
We can write an expression for the momentum:
$\lambda = \frac{h}{p}$
$p = \frac{h}{\lambda}$
Since $\lambda$ is greater in a finite well, then the magnitude of the momentum $p$ is less in a finite well.
In a finite well, the magnitude of the momentum is less than it would be if the potential well were infinite.
