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an electrion with mass 9.11e031 kg has momentum 4e-22. what is its kinetic energy

the answer is 6.3e-14 J but i have no idea how to get here

relativity kinetic energy = (y-1)mc^2 where y = 1/(square root of 1-(v^2/c^2)

momentum = ymu

thats as far as i can get , how the hell can u solve this type of problem if they dont give u the velocity of the electron?

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# Homework Help: Help relativity exam in in 5 hours

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