# Homework Help: Webassign even my ta's didn't know what to do ? and im in intro to physics

1. Feb 6, 2009

### phys-lexic

webassign even my ta's didn't know what to do... ???... and im in intro to physics

1. The problem statement, all variables and given/known data
A 33 ohm resistor is made from a coil of Cu wire whose total mass is 12g. (a)What is the diameter of the wire and (b) how long is it ? ( give you answer in m)

2. Relevant equations
one equation my ta tried to use was (R) = (resistivity) x (L/A)

3. The attempt at a solution
no idea... we cant figure out where to go because the equation has both length and radius (in the equation for A of the cross section of the wire) as variables... this is the only question left on my webassign and i have 30 mins left... please help

2. Feb 6, 2009

### Dick

Re: webassign even my ta's didn't know what to do... ???... and im in intro to physic

There is a mass in the problem. There's a second equation that says mass=density*volume=density*length*area.

3. Feb 6, 2009

### americanforest

Re: webassign even my ta's didn't know what to do... ???... and im in intro to physic

Two equations, two unknowns. Solve:

$$R=\rho \frac{L}{A}$$ and $$m=dV=dAL$$ where d is density and rho is resistivity