Air Balloon Ballast Q: Find Weight to Rise 105m in 15s

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Homework Help Overview

The discussion revolves around a problem involving a lighter-than-air balloon that needs to rise a specific distance within a set time frame. Participants are exploring the relationship between the balloon's buoyancy, the weight of the ballast, and the forces acting on the balloon, given the radius of the balloon and the density of air.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning, Assumption checking

Approaches and Questions Raised

  • Participants are attempting to calculate the volume of the balloon and its mass while stationary. They are questioning how to derive the force required for the balloon to rise and how the mass of the balloon relates to the buoyant force and the weight of the ballast that needs to be dropped.

Discussion Status

The discussion is ongoing, with participants raising questions about equilibrium between buoyant and gravitational forces. Some have suggested that the mass of the balloon should equal the density of air times its volume, indicating a productive line of reasoning.

Contextual Notes

There is a mention of a trick in the problem regarding the mass of the balloon and the mass jettisoned, which suggests that assumptions about the system's dynamics are being examined.

KingTutATL
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A lighter than air balloon and its load of passengers and ballast are floating stationary above the eart. Ballast is the wieght that can be dropped overboard to make the balloon rise. The radius of this balloon is 6.25m. Assuming a onstant value of 1.29 kg/m^3 for the density of air, determine how much weight must be dropped overboard to make the balloon rise 105m in 15.0s?

I've been working on this one for a while and just keep getting nowhere!
 
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KingTutATL said:
A lighter than air balloon and its load of passengers and ballast are floating stationary above the eart. Ballast is the wieght that can be dropped overboard to make the balloon rise. The radius of this balloon is 6.25m. Assuming a onstant value of 1.29 kg/m^3 for the density of air, determine how much weight must be dropped overboard to make the balloon rise 105m in 15.0s?

I've been working on this one for a while and just keep getting nowhere!
What is the volume of the balloon? What is the mass of this balloon if it is floating stationary above the Earth (not accelerating)?

What force is required for the balloon to rise 105 m in 15.0 seconds (careful: there is a bit of a trick, because the mass of the balloon accelerating depends on how much mass you drop overboard - work out an algebraic expression for the force in terms of the mass of the balloon and the mass jetisoned).

What mass must the balloon have in order to generate that buoyant force?

AM
 
How do I calculate the mass of the balloon while it is stationary. I guess it would be in equilibrium with the force of gravity and the buoyant force that oppose each other.
 
KingTutATL said:
How do I calculate the mass of the balloon while it is stationary. I guess it would be in equilibrium with the force of gravity and the buoyant force that oppose each other.
If there is no acceleration, the buoyant force and the weight of the balloon balance. What does this mean for the mass of the balloon divided by volume?

AM
 
That they should equal the density of the air!
 

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