The oven draws 1100W of power, and you have determined that it heats with an efficiency of 51%. Using this information, determine the time t it would take to bring 240mL of water from 25C to 100C . Note that 4.2 J of energy is required to raise the temperature of 1.0mL of water by 1.0C.

Answer 1

.51 * 1100 = 561 Watts = 561 Joule/second

561 t = heat in
= 240 mL * (75 deg C) (4.2 Joule/mLdegC)

so
t = 240*75*4.2/561
=135 seconds
about 2 minutes and 15 seconds
This must be a microwave oven.