$(4)$ A muon is a subatomic particle with the same charge as an electron, but a mass $206\mathrm{.}8$

times larger than an electron. Evaluate the de Broglie wavelength of the muon if it has been

accelerated from rest through a potential difference of $500\mathrm{.}0$ million volts.

$($The answer is $2\mathrm{.}079$ fm$)$