# Homework Help: Volume/volume and weight/weight persentages of the constituents in a composite

1. Mar 10, 2009

### mitnord

Hi,

I have an aluminium/lead composite material with density of 8,3 g/m^3. How do I find volume/volume and weight/weight persentages of aluminium and lead in the material, if the masses of the composites are not given?

The volume of the material is also not known.

Thanks.

2. Mar 10, 2009

### Carid

You don't need to know the volume since the density is independent of volume.

8,3 grams per cubic metre sounds remarkably small for something involving metals!

You know Archimedes sorted this out for a king who wasn't sure that his crown was pure gold or alloyed with silver.

(DensityAl * VolumeAl) + (DensityPb * VolumePb) = (AverageDensity * TotalVolume)

VolumeAl + VolumePb = TotalVolume

Assume TotalVolume to be one cubic metre. You know the three densities (or you can look them up) so you've got two equations and two unknowns.

From that you can work out the ratios you are looking for.