# Rho hollow cylinder

1. Mar 25, 2012

### mtje

1. The problem statement, all variables and given/known data

rho of a hollow cylinder can be found with 4 measured quantity by the folowing formula, proof this formula

2. Relevant equations

ρ= 4.m
∏.(d²-D²).h

d is the outside diameter and D the inside

3. The attempt at a solution

since it's my first time ever taking physics classes i'm kinda stuck
(well first time taking science classes)

ρ=m
V

so the formula of the hollow cylinder is V=∏.(d²-D²).h

the 4.m should be the mass but don't realy get what the 4 is standing there for

Could someone explain me how i should solve this ore give me a helping hand with the beginning of it?

2. Mar 25, 2012

### OldEngr63

The formula for the area of a circle is

A = π r2 = (π/4) d2

where r = radius and d = diameter.

When you have a hollow circle, the same sort of thing still applies, just with a difference of squares. But notice the (π/4) stays out in front.

If you think this on through, you will see where the rest of your expression comes from.