Past exam of the short options paper shared by Prelims and Parts A and B of the physics course of the University of Oxford / 2015 / S3 / 2 / 2

For the macroscopic mass,The ideal fixed-momentum expression tends to infinity as $v\to 0$. An everyday localized object is not a perfectly coherent momentum eigenstate, however: its thermal and environmental momentum uncertainty remains nonzero, and decoherence rapidly suppresses spatially separated coherent alternatives. Merely setting the mean velocity to zero does not prepare an object with a macroscopic coherence length.