thin walled tank having a total surface area of 150m2 contains 0.8m3 water at 350K. It is Lagged with 150mm Layer of material of thermal conductivity of 4x10^-2W/mK The temperature of the outside surface of the thin walled is 290K what electrical power be applied to an immersion heater to maintain the temperature of 350K (assume the thickness of the walls to be negligible) If the heater were switched off, how long would it take for the temperature of the hot water to fall to lK. (Specific heat capacity of water is 41707J/kgK, density of water is 1000kg/m3)