Calculate Minimum Volume for Balloon Lift Off w/ Helium & Load

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Homework Help Overview

The problem involves calculating the minimum volume required for a helium-filled balloon to achieve lift-off, given the densities of helium and air, the mass of the empty balloon, and the load it must lift. The context is rooted in principles of buoyancy and fluid dynamics.

Discussion Character

  • Exploratory, Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • Participants discuss the relationship between the weight of the displaced air and the total weight of the balloon and load. There are attempts to apply Archimedes' principle and clarify the conditions for lift-off. Questions arise regarding the equivalence of volumes and the role of helium in the calculations.

Discussion Status

The discussion is ongoing, with participants seeking clarification on the principles involved and how to set up the equations correctly. Some guidance has been offered regarding the relationship between the weights and volumes, but confusion remains about specific terms and assumptions.

Contextual Notes

Participants note that the balloon material and load occupy negligible volumes, which is a key assumption in the problem. There is also uncertainty about how to incorporate the mass of helium into the overall calculations.

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Homework Statement


A balloon is to be filled with helium(density = 0.178kg/m^3) while the air outside has density of 1.29km/m^3. The mass of the empty balloon is 80.0kg and it is to lift a load of 240kg. What minimum volume is necessary for the lift off? Assume that the balloon material and the load occupy negligible volumes.


Homework Equations



density = M/V

The Attempt at a Solution



I'm not quite sure how to start with this question. Can someone help me please?
 
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The balloon will float when the weight of the displaced air is equal to the weight of the balloon with load.

Volume of the balloon = mass of the balloon/density of helium.
 
hmmm. not quite getting it.

This is archemides' principle right? so wouldn't the equation be:

density of balloon/ density of gas = volume of gas/ volume balloon??
 
Mass of the displaced air = Ma = (240 + 80 + VHe* ρHe) kg.

volume of the air = Ma/ρa = ... = Volume of the balloon.

So Vb*ρa = (240 + 80 + VHe* ρHe) kg

Ηere volume of the balloon is equal to the volume of He.
 
k...just want to clarify. The balloon will float when the mass of the displaced air is equal to the weight of the balloon plus the load.

therefore,
Ma = (240 + 80)kg including helium??

how come is volume of air = volume of balloon?

sorry...a bit confused. I'm not great with this kind of physics.
 
mizzy said:
k...just want to clarify. The balloon will float when the mass of the displaced air is equal to the weight of the balloon plus the load.

therefore,
Ma = (240 + 80)kg including helium??

how come is volume of air = volume of balloon?

sorry...a bit confused. I'm not great with this kind of physics.

(240 + 80)Kg is mass without helium. Mass of the displaced air is equal to the (mass of helium + 240 + 80) kg. Balloon will float only when it is filled with the helium. Since the balloon material and the load occupy negligible volumes, volume of the helium = volume of the air.
 

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