an electron has a kinetic energy that is 1.8 times its rest energy. What is its speed, expressed as a fraction of the speed of light?

Answer 1

m•c^2 = 1.8•m(o) •c^2,
m(o) •c^2/sqrt(1- β^2) = 1.8•m(o) •c^2,
sqrt(1- β^2) =1/1.8
β = 0.831
β = v/c ,
v = 0.831c = 2.49•10^8 m/s