JEE Advanced 2016 Paper 1

A water cooler of storage capacity 120 liters can cool water at constant rate of P watts. In a closed circulation system (as shown schematically in the figure), the water from the cooler is used to cool an external device that generates constantly 3 kW of heat (thermal load). The temperature of water into the device cannot exceed 30°C and the entire stored 120 liters of water is initially cooled to 10°C. The entire system is thermally insulated. The minimum value of P (in watts) for which the device can be operated for 3 hours is :(Specific heat of water is 4.2‌kJ‌kg–1K–1and the density of water is 1000‌kg‌m–3)