Fluids Question Regarding Density

In summary, the conversation discusses the calculation of the buoyant force on a spherically shaped balloon filled with helium and its ability to lift cargo. After some unsuccessful attempts, the conversation suggests drawing a free-body diagram and applying Newton's second law to accurately determine the buoyant force. The equation Fb = (Mhe+800kg)g is used, but is questioned for its accuracy due to the units of mass and gravity. The conversation ends with the suggestion to not take shortcuts and to become more familiar with physics.
  • #1
davidkis
8
0

Homework Statement



A spherically shaped balloon has a radius of 11.5 m, and is filled with helium. How large a cargo can it lift, assuming that the skin and structure of the balloon have a mass of 1200 kg?
Neglect the bouyant force on the cargo volume itself.

Homework Equations


Fb = (Mhe+800kg)g


The Attempt at a Solution


I used the above equation to determine the buoyant force acting on the balloon but didn't seem to work. I tried some other methods but i can't get how much it can lift. Need some explanation thanks.
 
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  • #2
What's the equation for the buoyant force on ANY object in ANY fluid? After getting that, draw a free-body diagram on the balloon and note that buoyancy must balance gravity if the balloon is to lift the heaviest possible load.
 
  • #3
still can't get it...seems like a easy question too.. i am setting Fb = 1200+m+g. I got force buoyant to be density of air (1.29 kg/m3) * Gravity * Volume. Which looks like 1.29*9.8*3583.477 = 1200+m+g. m is the mass of the cargo which i am solving for. i keep getting the mass of the cargo to be 3422.68 which is wrong. any ideas of where I'm messing up?
 
  • #4
where did you get Fb=1200+m+g? It doesn't make sense because m has units of kg, while g has units of m/s^2.

Anyhow, draw a free-body diagram. Label all forces. Then write out Newton's second law. Don't take any shortcuts until you get more familiar with physics.
 

What is density and how is it measured?

Density is a measure of how much mass is contained in a given volume of a substance. It is typically measured in units of mass per volume, such as grams per milliliter or kilograms per cubic meter. To measure density, you need to know the mass of the substance and its volume. The density can then be calculated by dividing the mass by the volume.

What factors affect the density of a fluid?

The density of a fluid is affected by its temperature and pressure. Generally, as the temperature of a fluid increases, its density decreases. This is because the molecules in the fluid are moving faster, causing them to spread out and take up more space. Pressure also affects density, as compressing a fluid will increase its density.

How does density impact the behavior of fluids?

Density plays a key role in the behavior of fluids. Heavier, more dense fluids will sink below lighter, less dense fluids. This is why oil floats on top of water, as oil is less dense than water. Density also affects the flow of fluids, as denser fluids will flow more slowly than less dense fluids.

What is the difference between density and viscosity?

Density and viscosity are both properties of fluids, but they measure different characteristics. Density is a measure of how much mass is in a given volume of a substance, while viscosity is a measure of a fluid's resistance to flow. In other words, density is a measure of how tightly packed the molecules in a fluid are, while viscosity is a measure of how easily the molecules can move past each other.

How does the density of a fluid affect objects that are submerged in it?

The density of a fluid determines whether an object will sink or float when submerged in the fluid. If the object is less dense than the fluid, it will float. If the object is more dense than the fluid, it will sink. This is why a beach ball will float on water, but a rock will sink. The density of the fluid also affects the amount of buoyant force acting on the object, which can change the object's apparent weight while submerged.

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