And it rises during clear and sunny days. If the pressure between the two extrem

Question

And it rises during clear and sunny days. If the pressure between the two extreme conditions is given to be 0.2 in of mercury, determine how much the boiling temperature of water will vary as the whether changes from one extreme to the other. A person cooks a meal in a 30 - cm - diameter pot that is covered with a well - fitting lid and lets the food cool to the room temperature of 20 degree C. The total mass of the food and the pot is 8kg. Now the person tries to open the pan by lifting the lid up. Assuming no air has leaked into the pan during cooling, determine if the lid will open or the pan will move up together with the lid. Water is boiled at 1 atm pressure in a 25 - cm - internal - diameter stainless steel pan on an electric range. If it is observed that the water level in the pan drops by 10 cm in 45 min, determine

Explanation / Answer

If there was significant water in the food, it will have [partially] boiled into steam during the cooking. The steam would escape by lifting the lid, and would have carried some or all of the air with it [depends on how much water boiled]. Then while the pot cools the steam will condense, leaving a partial vacuum in the pot, at a pressure equal to the vapor pressure of water at 20 C [assuming all of the air was swept from the pot by steam escaping while cooking]. Force = pressure times area. You know the vapor pressure of water at 20 C or can look it up ior calculate it. You know atmospheric pressure. Take the difference and multiply it by the area of the lid [watch you units !] to get the force holding the lid to the pot. Compare that force with the weight [Mg where g = 9.8 m/s/s] of the pot.

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