- #1

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The question is: What is the momentum, in conventional SI units, of a proton of momentum 685 MeVc

^{-1}?

So, I tried two methods which yielded slightly different answers, both proximate to the actual answer (3.66 x 10

^{-19})

What I first tried to do was to rearrange: ρ=γm

_{0}v

To find the particles velocity and then multiply it by the proton's rest mass in kg. I got 2.995 x 10

^{-19}kgms

^{-1}

The second method, which gave me the result 3.45 x 10

^{-19}kgms

^{-1}was the following:

From: E

^{2}= (m

_{0})

^{2}c

^{4}+ p

^{2}c

^{2}I got a value for total energy. I then subtracted the rest energy from that and I got a value for KE.

I equalled that to p

^{2}/2m and solved for p (using m in kg and the energy converted from MeV to J)

Are my answers wrong? The book says 3.66 x 10

^{-19}and I simply can't get that!

Thanks in advance!