An open vessel contains 0.5 kg of ice at -20 degree Celsius. The mass of the container can be neglected. Heat is supplied to the vessel at constant rate of 420 J/min for 500 min.
(a) After how many minutes does the ice start to melt?
(b) After how many minutes does the temperature start to rise above 0 degree Celsius?
(c) Plot a curve showing the elapsed time as abscissa and the temperature as ordinate.