The expression for the energy in special relativity is:
E = gm0c2
where g = [1 - (v2/c2)]
and m0 is the rest mass of the particle, in this case, an electron.

8.83X10-13 = g(9.1X10-31)(3X108)2

g = 10.78

 [1 - (v2/c2)] = (1/10.78)2 = 0.00860

 (v/c)2 = 1 - 0.00860 = 0.991397

 Therefore v = 0.996c

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