# Archimedes' principle

1. Apr 20, 2005

### heather32283

Probably an easy question, just can not figure it out.
A duck is floating on a lake with 25% of its volume beneath the water. What is the average density of the duck?

To me it seems like they do not provide enough information to figure the problem out, Im soo stuck.

2. Apr 20, 2005

### whozum

I think all you need is the density of water, which is 1000kg/m^3

3. Apr 20, 2005

### heather32283

yea I know that but I can not figured out the forula in which to use

4. Apr 20, 2005

### OlderDan

The weight of the water displaced by the duck is equal to the weight of the duck. How does the volume of the displaced water compare to the volume of the duck?

5. Apr 20, 2005

### heather32283

its equal also isnt it

6. Apr 20, 2005

### Spectre5

The duck's volume is V, the amount of volume displaced is equal to the amount of volume under the surface, so .25*V

7. Apr 20, 2005

### heather32283

ok got that part, just confused

8. Apr 20, 2005

### Spectre5

can you do the rest of the problem then?

9. Apr 20, 2005

### heather32283

so we would just use the mass density equation right

10. Apr 20, 2005

### Spectre5

for a floating object, the bouancy force is equal to the weight of displaced water.

density(duck)*g*V(duck) = density(fluid)*g*V(displaced)