Question

It takes 56.5 kilojoules of energy to raise the temperature of 150 milliliters of water from 5°C to 95°C. If you

use an electric water heater that is 60% efficient, how many kilojoules of electrical energy will the heater
actually use by the time the water reaches its final temperature?

Answer 1

If 56.5kJ are needed to raise the temp by 90°C and if the heater is 60% efficient that means that:
60% X y = 56.5kJ
where y is the electrical energy in kJ that the heater will use.
y = 94.2kJ