A perfectly insulated enclosure containing a heater is filled with a liquid having thermal capacitance C. The temperature of the liquid is assumed to be uniform and is denoted by theta. The heat supplied by the heater is q(t). a) write the differential equation obeyed by the liquid temperature theta. b) solve the equation you found in part (a) for theta in terms of the arbitrary initial temperature theta(0). c) sketch theta versus t when q_i(t) = 1 for 10 < t < or equal 20 and zero otherwise.