Homework Help: Basic bouyancy

1. Jan 1, 2008

cammarata123

1. The problem statement, all variables and given/known data

I have a balloon with helium in it, I need to know the acceleration that it rises. It would be great if you could tell me what I need if I am missing any. This is what I have,

Density of liquid(air) = 1 g/l
Density of Helium = .1786 l/g
Volume of Balloon = 91 cubic centimeters

I need to know the velocity upwards as I change the Density of the Balloon

2. Relevant equations

3. The attempt at a solution

I got the 91 cubic centimeters, also figured out .1786, other than that... horrible failure, like 1000 meters per second

2. Jan 1, 2008

Staff: Mentor

What forces act on the balloon? What's the net force?

What's the mass of the balloon?

Apply Newton's 2nd law.

(You won't need the velocity of the balloon to find its acceleration.)

3. Jan 1, 2008

cammarata123

to find the mass I need the weight, I don't have the physical balloon, how can I figure out using the percentage of helium as a variable how much it weighs? then I can multiply times 9.8 and get the mass? I think it was a mistake taking a.p physics, it is so tough for me

4. Jan 1, 2008

Staff: Mentor

You have the volume and the density, so you should be able to find the mass of the helium. (Ignore the mass of the balloon material itself--assume it's zero unless you are given it.)

5. Jan 1, 2008

cammarata123

I found out a better way to ask the question. Do you know of a way to calculate acceleration as a function of density?

6. Jan 1, 2008

Staff: Mentor

You'd figure out the acceleration in the same manner that I described above.

What information are you given?

7. Jan 1, 2008

cammarata123

It's a science fair, I am see'ing the effect of helium on a balloon in air

8. Jan 1, 2008

cammarata123

can I have an equation to find the mass of the helium? then using that, find acceleration

9. Jan 1, 2008

Staff: Mentor

What equation relates density to mass and volume? (What's the definition of density?)

10. Jan 1, 2008

cammarata123

d = m/ v

mass per unit if volume

11. Jan 1, 2008

cammarata123

of volume*

12. Jan 2, 2008

cammarata123

I got an A on my science fair checkup! thanks so much