Menengai Geothermal Company intends to drill power holes to generate power from the underground steam from dry rock granite at Menengai farm. As an engineer in charge, determine the following: (i) The useful heat content per square kilometer of dry rock granite to a depth of 7 km. Take the geothermal temperature gradient at 40 oC per kilometer, the minimum useful temperature as 140 K above the surface temperature, the rock density as 820 J/KgK and the rock thermal capacity as 820 J/KgK. (ii) The time constant for useful heat extraction with a pumped water extraction of 100 litres per sec. per kilometer.