PHYSICS · Single correct · A Level · Physics · Particles and radiation · Particles and radiation
Problem
A 0.145kg baseball traveling at 40ms−1 has a diameter of 7.4cm. Which of the following best explains why its motion can be described accurately using classical mechanics rather than quantum mechanics?
(a) Its speed is far below the speed of light, so Newtonian mechanics is automatically valid.
(b) Repeated collisions with air molecules rapidly collapse its wavefunction, forcing it to travel along a single classical trajectory.
(c) Its de Broglie wavelength is many orders of magnitude smaller than its diameter, so any wave characteristics average out and are unobservable.
(d) Because its momentum is enormous compared with Planck’s constant, the uncertainty in its position can be taken as zero, justifying a classical description.