a i. Explain what is meant by internal energy.
ii. Explain what is meant by the absolute zero of temperature.
b. An electric hot water heater has a power rating of 9.0 kW. The water is heated as it passes through the heater. Water flows through the heater at a speed of 1.2 m s⁻¹ through pipes that have a total cross-sectional area of 4.8 × 10⁻⁵ m². The temperature of the water entering the heater is 15 °C.

i. Calculate the mass of water flowing through the heater each second.
ii. Calculate the temperature at which the water leaves the heater.
iii. State any assumptions you have made in your calculation.
iv. It is possible to adjust the temperature of the water from the heater.

Suggest how the temperature of the water could be increased without increasing the power of the heater.

(Density of water = 1000 kg m⁻³; specific heat capacity of water = 4200 J kg⁻¹ °C⁻¹.)