How do I find the velocity when I already have kinetic energy (power) and mass?

KE = 0.5mv^2

2KE = mv^2

2KE / m = v^2

v = sqrt(2KE / m)

In the formula for kinetic energy, it's is only the velocity that is squared, not the mass as well.

Kinetic energy is just that, energy, NOT power. Power is a measure of energy per unit time. Energy is measured in joules (J), power is measured in watts (W = J/s).

Lava is correct. But if you truly have the power P = KE/t; then you need to find KE = Pt = 1/2 mv^2 before you solve for v = sqrt(2KE/m). Did the problem also give you an interval of time t the system was moving? If so and power in Joules/sec ~ Watts was given, you need to find energy KE = Pt before solving for v.

Otherwise, you should understand that KE (power) is inconsistent. Energy is in Joules while power is in Joules/sec or Watts. So implying KE and "power" are the same thing, is incorrect.

Also might I suggest you learn to type equations using variables and operators. That will avoid a lot of ambiguity and/or errors like lava has indicated earlier. I can guarantee you'll get more and better answers when you do.

velocity=root under(2xK.E./mass)

Now it will give a positive and a negetive value. Choose the relevent one.