An ice cube placed in microwave melts in five minutes and it takes 3.50 kj of energy to melt it. what is the power of the microwave?

If the ice absorbed 350,000 joules in 5 minutes, then it absorbed energy

at the rate of

(350,000 joules) / (5 x 60 seconds) = 1,166-2/3 watts.

Surely the ice cube didn't absorb every joule delivered to the cooking chamber,

so the microwave oven's cooking power had to be significantly more than that.