Find the resistance between the top and bottom faces of the cylinder

[mba444]

Homework Statement

A 361 g mass of aluminum (Al) is formed into
a right circular cylinder shaped so that its
diameter equals its height.
Find the resistance between the top and
bottom faces of the cylinder at 20◦C. Use
2700 kg/m3 as the density of Al and
2.82 × 10−8 OHM· m as its resistivity. Answer
in units of
OHM.

Homework Equations

R= raw *(L/A)
D=(m/v)
height = diameter ... therefore r will (h/2)
V=pi*r^2*h

The Attempt at a Solution

what i did is that i solved for the height by substituting it in the density problem getting D(given)= M(given)/(Pi*(h/2)^2*h) .. which after solving is h= (1.444/(2700*Pi))^(1/3)
after that i substitute it back into the resistance equation.


Im stuck ad i eed your help please
thanx i advance

 

[tiny-tim]

Hi mba444!

(have a pi: π and a rho: ρ and try using the X² tag just above the Reply box )

… what i did is that i solved for the height by substituting it in the density problem getting D(given)= M(given)/(Pi*(h/2)^2*h) .. which after solving is h= (1.444/(2700*Pi))^(1/3)
after that i substitute it back into the resistance equation.

Well, that looks ok so far …

what number did you get, and what did you get next? ​

 

[mba444]

i got for h .. 0.0554m
after substituting into the R equation i got 1.169e-7


but my answer is wrong !

 

[drizzle]

I think you need to use the Callendar–Van Dusen equation [which is a relation between temperature and resistance]

 

[tiny-tim]

i got for h .. 0.0554m
after substituting into the R equation i got 1.169e-7

I get your h, but not your R …

how do you get 1.169e-7 ?

 

[mba444]

ignore the previous value i think its a calculation mistake
i calculated it again i got 3.65586e-8
is it right ??

 

[tiny-tim]

ignore the previous value i think its a calculation mistake
i calculated it again i got 3.65586e-8
is it right ??

how did you get it?

 

[mba444]

R= (2.82e-8)[(0.055)/(PI*(2*0.055)^2)]

radius = 2* h

 

[tiny-tim]

R= (2.82e-8)[(0.055)/(PI*(2*0.055)^2)]

radius = 2* h

uhh? radius = h/2

(and what happened to that π I gave you?)

 

[mba444]

ya since in the question they told us that the height equal the diameter

 

[mba444]

i really don't understand .. my home work is due today .. and i really feel lost

 

[Redbelly98]

Homework Equations

R= raw *(L/A)

What values are you using for raw, L, and A?