Question: The latent heat of vaporization of liquid nitrogen is about 200 kJ/kg. Suppose you have 6 kg of liquid nitrogen boiling at 77 K. If you supply heat at a constant rate of 45 W via an electric heater immersed in the liquid nitrogen, how long will it take to vaporize all of it? What is the time for 6 kg of liquid helium, whose heat of vaporization is 20.9 kJ/kg?