Assertion (A): An electron and a proton, each starting from rest, are accelerated through the same potential difference of $200\ \text{V}$. The de Broglie wavelength of the electron is about $43$ times that of the proton. Reason (R): Each particle gains the same kinetic energy $eV$, and for a given kinetic energy the momentum of a particle is proportional to the square root of its mass.