You’re strolling through the park on a sunny weekend when you see a vendor selli
ID: 1838978 • Letter: Y
Question
You’re strolling through the park on a sunny weekend when you see a vendor selling balloons. Your mind immediately turns to CE340 and you cancel the rest of your plans to start a buoyancy experiment (who wouldn’t?). You buy a 0.5m diameter, approximately spherical balloon that is filled to 7 kPa gage pressure. Without helium, the balloon has a mass of 2 grams, and the balloon is TURQUOISE.
(a) At ground level (assumed to be at sea level), what is the density of the helium in the balloon? Assume an air temperature of 20 and be sure to use the appropriate specific gas constant. (Answer is 0.178 kg/m^3 - how?)
b) You want to release the balloon and have it rise until it reaches a terminal elevation at the base of the stratosphere. How much weight must you tie to the balloon to make this happen? Assume that the balloon diameter remains constant and be sure to include the mass of the helium in your calculation. Assume that the atmosphere’s properties are well-described by the “U.S. Standard Atmosphere”, as given in your text. (Answer is 10g - how?)
(c) Explain why the balloon reaches a terminal elevation. Hint: The helium inside the balloon has the same temperature as the air outside the balloon.
Explanation / Answer
a)
Maximum net force acxting on a person standing on the earth is gravitational force which is equal to weight.
if the mass is 60 kg
so weight W = mg = 588 N
b)
After a certain height above the earth, there is no gravitational effect. because person mass is negligible compared to the masses of the planets
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