An eletric press consumes 120kj of energy in 5 minutes, when the magnitude of current flowing through it is 2a. calculate the electric potential at which press operates.

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".