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Upthrust - undergraduate - Confirm answer please Watch

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    Hey guys, could you please confirm my answers and your input will be much appreciated.

    A gas filled Zeppelin airship of the 1920’s had a volume of 1.9 x 105 m3. Calculate the upthrust on the Zeppelin due to the surrounding air (air density is 1.20 kgm-3).
    Calculate the weight (not mass!) of hydrogen gas inside the Zeppelin (density 0.090 kg/m3) if 90% of the Zeppelin’s volume was filled with hydrogen.
    From these two calculations, estimate what the weight of the Zeppelin itself would have been , assuming the upthrurst was just enough to keep the airship floating at a level height.
    Later airships were filled with helium gas instead of hydrogen even though helium has a density of 0.18 kg/m3. Why was this done?

    1. The upthrust i got was (1.9*10^5) * 1.2 * 9.81 = 2236680N

    2. The weight of hydrogen gas i got was 0.9(1.9*10^5) * 0.09 * 9.81 = 150975.9N

    3. The weight of the submarine would therefore be 2236680 - 150975.9 = 2085704.1N

    4. The reason for the change of hydrogen and helium, i wrote that the submarine will weigh less if helium is used and therefore the submarine will be faster when moving.


    Could someone please confirm these results as i do not hold the answer sheet - many thanks!
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    (Original post by Dontay)
    Hey guys, could you please confirm my answers and your input will be much appreciated.

    A gas filled Zeppelin airship of the 1920’s had a volume of 1.9 x 105 m3. Calculate the upthrust on the Zeppelin due to the surrounding air (air density is 1.20 kgm-3).
    Calculate the weight (not mass!) of hydrogen gas inside the Zeppelin (density 0.090 kg/m3) if 90% of the Zeppelin’s volume was filled with hydrogen.
    From these two calculations, estimate what the weight of the Zeppelin itself would have been , assuming the upthrurst was just enough to keep the airship floating at a level height.
    Later airships were filled with helium gas instead of hydrogen even though helium has a density of 0.18 kg/m3. Why was this done?

    1. The upthrust i got was (1.9*10^5) * 1.2 * 9.81 = 2236680N

    2. The weight of hydrogen gas i got was 0.9(1.9*10^5) * 0.09 * 9.81 = 150975.9N

    3. The weight of the submarine would therefore be 2236680 - 150975.9 = 2085704.1N

    4. The reason for the change of hydrogen and helium, i wrote that the submarine will weigh less if helium is used and therefore the submarine will be faster when moving.


    Could someone please confirm these results as i do not hold the answer sheet - many thanks!
    The maths is ok but you need to read the question.
    It says the Zeppelin was an airship. Not a submarine.
    There was a famous tragedy relating to the Zeppelin in 1937 where one caught fire and exploded, killing many people.
    A quick wiki search will find it.
    It will also tell you the cause and why hydrogen was changed to helium.
 
 
 
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