3. A closed system undergoes a process during which there is energy transfer from the system by heat at a constant rate of 10 kW, and the input power varies with time according to: (8t 0< t < 1h W 8 t > 1 h where t is time, in hour (h), and W is in kW. (a) What is the time rate of change of system energy at t = 0.6 h, in kW? (b) Determine the change in system energy after 2 h, in kJ.