Question

You have two solid blocks of metal wrapped in paper. The blocks are the same size, but one is pure aluminum and the other is pure iron. You know that iron has a greater density than aluminum. How can you identify each without removing the wrapping? Explain.

Answer 1

Answer:

We can identify easily which block has more density, if we try to lift each one, and the heavier will be the one with more density. In this case the block of iron will be the one with more density.

Explanation:

To understand this we will give some numerical values to give the best explanation of this situation.

Let's say that we have the two blocks over one table, and over the table there is a special scale to measure the mass of an object.

Both block have the same dimensions, and seaching information of density by internet we find that the density for the iron is 7850 [kg/m^3], and the density for the aluminum is 2712 [kg/m^3]

Now the dimension of each bloack are 10*10*10 [cm] so, the volume will be 1000 [cm^3] = 0.001[m^3]

Now using the expression of density:

$density = \frac{m}{v} \\where:\\m = mass [kg]\\v= volume [m^{3} ]\\m = density* volume$

for the iron

$miron=7850*0.001 = 7.85 [kg]$

for the aluminum

$malumi=2712*0.001=2.712[kg]$

Therefore the weight of the iron will be always almost 3 times heavier than the weight of the aluminum.