A cup of coffee is heated in a microwave oven. If the mass of coffee (modeled as liquid water) is 0.2 kg and the rate of heat transfer is 0.1 kW.
(a) Determine the rate of change of internal energy (u).
(b) Assuming the density of coffee to be 1000 kg/m3 and the specific internal energy in kJ/kg to be related to temperature through u = 4.2T, where T is in Kelvin, determine how long it takes for the temperature of the coffee to increase by 20oC.