An argon atom has a mass of 6.64 x 10kg has 5.5 x 108J of kinetic energy. At what velocity is it moving.?
Use the definition of kinetic energy and solve for V.
K.E. = (1/2) M V^2
You'd better correct your mass M of the argon atom before you do the calculation. You left out an exponent.
I suspect your kinetic energy exponent has a minus sign left out. Otherwise you would have to have a velocity close to the speed of light.