This theorem's namesake also gives his name to a paradox involving the Lorentz contraction of a rigid rotating disk, and it can be derived by applying expectation values to the Lindblad equation. The particle-in-a-box initially appears to violate this theorem, which demonstrates the Bohr correspondence principle, since the probability of finding a particle at a wall is zero, so the expectation value of the force should vanish for any state. Therefore, it fails to be equal to the time derivative 
This theorem's namesake also gives his name to a paradox involving the Lorentz contraction of a rigid rotating disk, and it can be derived by applying expectation values to the Lindblad equation. The particle-in-a-box initially appears to violate this theorem, which demonstrates the Bohr correspondence principle, since the probability of finding a particle at a wall is zero, so the expectation value of the force should vanish for any state. Therefore, it fails to be equal to the time derivative of the momentum's expectation as this statement predicts. For 10 points, name this theorem, the quantum mechanical analog of Newton's Second Law, named for an Austrian friend of Einstein.
This theorem's namesake also gives his name to a paradox involving the Lorentz contraction of a rigid rotating disk, and it can be derived by applying expectation values to the Lindblad equation.
Ehrenfest's Theorem