Why Do We Convert MeV to Joules in Nuclear Physics Calculations?

[kenshi64]

(NOT HOMEWORK)Hey guys the question in the textbook goes like this:
Q) It is found that alpha particles with a KE of 7.7MeV bounce back off an aluminium target. If the charge of an aluminium nucleus is +2.1*10^-18C, calculate the velocity of the alpha particles(mass 6.7*10^-27kg).

http://www.rcnuwc.org/hl-answers/chapter7.html" is how the sum is solved (the first part, ignore the second part of the sum which I haven't posted).


MeV is converted into Joules and not left as MeV. But MeV is the unit of nuclear energy right. So because it is on a 'nuclear' scale is why we use the 'Joule' for the KE formula, since Joule is a a larger quantity suited to the formula? or just because 'simple' energy(non-nuclear) is in joules. I'm looking to know which of the assumptions is right. Thanks guys!

 

[LightHero]

The reason we use Joules for the KE formula is because energy is always measured in Joules, no matter what scale it is on. MeV is a unit of energy, but it is a much smaller unit than Joules and thus does not work with the KE formula. Regardless of whether it is nuclear or non-nuclear energy, Joules are always used as the unit of measurement.