Astirrer of shaft power 500w is used to stir 100 kg of water that is being heated. the heater output power is 3.5 kw and heat losses are 800w. the initial temperature of the water is 20°c. determine: (a) how long it will take before the water reaches a temperature of 80°c, (b) the internal energy change of the water. neglect the specific heat capacity of the vessel itself and take the specific heat capacity of water to be 4.19 kj/kgk.