# Time Dependence of Momentum Uncertainty for a Free Particle

Question: Show that in a free-particle wave packet the momentum uncertainty $$∆p$$ does not change in time.

I am not sure how to solve for the time derivative of the momentum uncertainty $$∆p$$. I am familiar with the derivation of the Heisenberg uncertainty principle but not aware of how to calculate the momentum uncertainty for a free particle (or its time independence). Can someone please direct me to the correct resources?