Phy 202
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I am doing the introductory problem set on modern physics and I am confused by this point
* The KE of the given electron in Joules is 90 eV * (1.6 * 10^-19 J / eV) = 1.44 * 10^-17 J.
We can find the momentum m v of the electron by multiplying its KE, which is .5 m v^2, by 2 m to obtain m^2 v^2, then taking the square root:
Wouldnt v=sq root(2KE/m)? Then we already have the mass of the electron so we can find momentum once we have velocity? This is from problem 4.
We could solve for v, then multiply m by v.
Or we could multiply KE by 2m and take the square root.
The latter is a slightly simpler calculation and illustrates an important relationship between KE and momentum. If we know KE and m, we can find mv without first finding m.