Can someone help me explain why are these answers wrong?

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Aleksander Krol
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can someone please tell me how are these wrong though? cause i'm not really getting it.. :/
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this question asked us to draw turbulent flow and i did and i don't get what went wrong in my drawing which led my teacher to not give any mark in this.
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"1) Density of air in the balloon is equal to the density of the surrounding air.
2) No resultant force upwards"
This answer is for part (b) of another question that asked, why does a hot air balloon stops rising. and it was for two marks, so i gave two reasons but i don't understand why was my first reason incorrect.
here are the questions of the above answers for which my marks were deducted. (just incase if anyone wanted to see for a better understanding)*
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i'm just trying to correct my errors so i don't repeat them again next time. i'd be grateful if anyone can help me explain my errors.
Last edited by Aleksander Krol; 1 month ago
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Pugsly
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Your answer regarding turbulent flow - you have written (b)(i), but the follow-up image shows that question as being (ii). Perhaps you have drawn the diagram in answer to the wrong question? It might seem petty but you may have omitted the uniform laminar flow's interference with a static object and resultant influence? It could be as simple as your diagram not seeming very clear.

As for your other question - as stated the density of the outside air decreases as the altitude increases, so the capacity and density of hot air within the balloon remains the same as you try to ascend. Combined with the weight constant of the hot air balloon itself, the difference in density is reduced to a point at which no further heating of air will create any more lifting force.

I know that's sort of what you were getting at, when you specifically said "equal" but it seems like it was asking for a more in depth explanation? Perhaps the appropriate equation, e.g. Archimedes principle or something.

I'm just guessing here, though. Maybe ask your lecturer?
Last edited by Pugsly; 1 month ago
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Aleksander Krol
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(Original post by Pugsly)
Your answer regarding turbulent flow - you have written (b)(i), but the follow-up image shows that question as being (ii). Perhaps you have drawn the diagram in answer to the wrong question? It might seem petty but you may have omitted the uniform laminar flow's interference with a static object and resultant influence? It could be as simple as your diagram not seeming very clear.

As for your other question - as stated the density of the outside air decreases as the altitude increases, so the capacity and density of hot air within the balloon remains the same as you try to ascend. Combined with the weight constant of the hot air balloon itself, the difference in density is reduced to a point at which no further heating of air will create any more lifting force.

I know that's sort of what you were getting at, when you specifically said "equal" but it seems like it was asking for a more in depth explanation? Perhaps the appropriate equation, e.g. Archimedes principle or something.

I'm just guessing here, though. Maybe ask your lecturer?
yessss you're right!! i regret making these careless mistakes :/ thank you anyways) have a good rest of the day!!
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Pugsly
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(Original post by Aleksander Krol)
yessss you're right!! i regret making these careless mistakes :/ thank you anyways) have a good rest of the day!!
No sweat, good luck in your studies mate.
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