# Not sure how to start this problem hint please!

1. Oct 9, 2005

### je55ica7

An empty rubber balloon has a mass of 0.0135 kg. The balloon is filled with helium at a density of 0.181 kg/m3. At this density the balloon is spherical with a radius of 0.300 m. If the filled balloon is fastened to a vertical line, what is the tension in the line?

I don't even know what equation to use...! AHH

2. Oct 9, 2005

### Tide

HINT: It's a question about buoyancy.

3. Oct 9, 2005

### je55ica7

is the tension equal to the force?

4. Oct 9, 2005

### lightgrav

yes, but there are several forces involved here. ...
all dealing with one Volume.

5. Oct 9, 2005

### Tide

Yes. The buoyant force is balanced by the tension in the string.

6. Oct 9, 2005

### je55ica7

so would i use the equation B=density(fluid) x volume(fluid) x g?

7. Oct 9, 2005

### Pyrrhus

Yes, substitute it in your $\sum F_{y} = 0$

8. Oct 9, 2005

### je55ica7

so it would be Density(Helium) x what volume? x 9.81 ?

9. Oct 10, 2005

### mukundpa

The forces acting on the balloon are gravity force, buoyant force and the tension in the line.

The buoyant force is applied by air of the atmosphere.

Buoyant force is equal to the weight of the displaced volume of the fluid.