A particular vacuum flask has a mass of 1 kilogram and contains 1 liter of liquid water. A heating element within the flask vaporizes the water, which exits through a nozzle on the mouth of the flask. (Assume the cap/stopper on the flask is massless and can be ignored.) The vapor escapes with a spreed of 25 meters per second relative to the tank. If all the vapor exits instantaneously:
(a) what is the speed of the empty flask? Assume its initial velocity is zero.
(b) how much energy did the heating element supply? You can disregard the energy needed to warm and vaporize the water.