Power = joules/second (watts)
(120,000 joules/5 minutes) x (minute/60 seconds) = 400 watts
Power dissipated by a component in an electrical circuit =
(current through it) x (potential difference across it).
400 watts = (2 amperes) x V
V = 400 watts / 2 amperes = 200 volts
Note:
That's the potential DIFFERENCE between the terminals of the machine,
NOT the "potential at which it operates".
