Question

The electric heating element in a 40-gallon water heater is rated at 4 kw. After your sister takes a shower, the water temperature has dropped to 90 degree F. How long will it take the heater to bring the temperature back up to 120 degree F? The density of water is 3.79 kg per gallon. neglect heat loss, which in a well-insulated heater should be a lot less than that 5-kw power input.

Answer 1