At the outset, it sounds like a silly question but scientifically speaking, it should be possible to heat a cup of water just by shouting. Boiling? I don't know, but let's see. (My favourite is that you can boil a cup of water by not doing anything! Yes - just leave a cup of water on your table, and wait for about 2 billion years; don't forget to top up the water as it evaporates. The Sun would have spent most of it's Hydrogen "fuel" and would be expanding to become a "red giant" with it's size extending to the orbit of Venus - Earth's temperature may be around 100°C . What more do you need?)



Back to shouting. An average person may be able to shout at around 100 dB - I

suppose you are an average person. Sound carries a relatively low amount of energy - consequently you may need to keep shouting for a long time. I suggested 100 dB, which may provide about .0001 watt of energy. Keep the frequency low - like under 1 KHz because lower frequencies of sound carry more energy, and you can save some time. If you were to focus this energy at the cup of water, you would probably be raising the temperature of the water by roughly 10^-6°C every second, give or take three zeroes. (sorry, I am not good at maths).



Don't forget, you need to keep shouting continuously until the water gets hot.



The standard room temperature is 25°C and you want to raise the temperature of the water to say, 50°C or more, I will leave you alone for about twenty years - you keep shouting 24/7 - and then check the temperature of the water, it would be around

63°C. If you really want to boil it, then you need to go up a mountain.



Good luck!