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Mangoes
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Homework Statement
What is the kinetic energy of an electron with a momentum of 40 GeV/c?
The Attempt at a Solution
Kinetic energy involves velocity of the particle so my first thought was to write momentum in terms of velocity.
[tex] p = \frac{mv}{(1-(v/c)^2)^{1/2}} [/tex]
[tex] p^2 = \frac{(mv)^2}{(1 - (v/c)^2)} [/tex]
[tex] p^2 - p^2v^2/c^2 = m^2v^2 [/tex]
[tex] p^2 - v^2(p^2/c^2 - m^2) = 0 [/tex]
[tex] v = \frac{p}{(p^2/c^2 - m^2)^{1/2}} [/tex]
From my understanding the statement is saying the electron's momentum is (40/c) GeV. Since 1 GeV = 1.602 x 10^(-10) J, I calculated momentum as (40)(1.602 x 10^(-10))/(c). This cancels the (m/s) unit from energy and now the value has units of momentum.
After looking up the mass of an electron and plugging in the numbers to find v, I got v = c, which is from my understanding impossible for an electron. The electron would have infinite kinetic energy.
What's off here? Would appreciate any insight.
EDIT:
I just realized I made a sign error. Mass in the final equation should have been + and not -.
Redid calculations though and v still is equal to c. Could this just be a problem where the actual number v is just ridiculously close to c and my calculator is rounding it up? Or am I just doing something plain wrong?
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