Examination-Style Questions. Density of Material Questions (b)(i)(ii)

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i have done few simple questions by using p = m/v to calculate the mass, volume and density, but for this question, i don't know how to do it. Please help ^^"
(a) Define the density of a material.
>Density is the mass of the material per unit volume.

(b)Brass, an alloy of copper and zinc, consists of 70% BY VOLUME of copper and 30% BY VOLUME of zinc.
Density of Copper = 8.9 x 10^3kgm^-3
Density of Zinc = 7.1 x 10^3kgm^-3

(i)Determine the mass of copper and the mass of zinc required to make a rod of bras of volume 0.80 x 10^-3m^3
hmm..Cu = Mass x 70% x 8.9 x 10^3kgm^-3, Zn = Mass x 30% x 7.1 x 10^3kgm^-3...?
(ii)Calculate the density of brass.
I think i will know how to do this question if i know the answer for (i)... = =
 
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oh yeah, for question (ii), should i just add up the two densities and divided by 2?...
 
54088 said:
oh yeah, for question (ii), should i just add up the two densities and divided by 2?...

If you're told that brass is made of 70% copper (by volume) and 30% zinc (also by volume), why would you expect the density of brass to be made of equal portions?
 
jdwood983 said:
If you're told that brass is made of 70% copper (by volume) and 30% zinc (also by volume), why would you expect the density of brass to be made of equal portions?

so what should i do?
 
Not to sound cryptic, but I'll answer your question with another question: If you had to make a piece of copper that that had a volume of [itex]0.8\times10^{-3} \mathrm{m^3}[/itex], how would you go about finding the mass required? And if the previous volume were to be made of only zinc, what would its mass be?