# Homework Help: Linear Mass Density

1. Oct 29, 2011

### brianna0404

Linear Mass Density!!

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

Find linear mass density using a graph ln(v) vs ln(T), from Velocity=squareroot Tension/linear density, take natural log ln(v) = 1/2 ln(T)-1/2ln(m). our professor told us to find it this way cause 1/2ln(m) is the y-intercept of the best fit line of five trials

2. Relevant equations
so y-intercept=-1/2ln(m). for y intercept I got 3.5073 from an experiment done in lab.

3. The attempt at a solution
I got 8.9866 * 10^-4 for linear mass density. but after all that my main question is what are the units? would they be m/s? if so how do I convert it to g/m?

Thanks!

Last edited: Oct 29, 2011
2. Oct 29, 2011

### EkaterinaAvd

Re: Linear Mass Density!!

it depends on units in which v and T are given. you have to extract units from formula Velocity=squareroot Tension/linear density.

Units of right and left parts of equation must be the same.

3. Oct 29, 2011

### brianna0404

Re: Linear Mass Density!!

the units for tension are newtons and the units for velocity are hertz times meters, which is just m/s. So i didn't know if taking the natural log of tension and velocity changes the units or are they the same?

4. Oct 29, 2011

### EkaterinaAvd

Re: Linear Mass Density!!

logarithm equation and equation without logarithm are eqivalent
if [v]=m/s, it doesn't mean that [ln(v)]=m/s of course. They are two different numbers representing the same velocity and can't have the same dimension.
but if you are consistent with formulas you have in your calculations, you will get right units from the initial equation.

because

ln(v) = 1/2 ln(T)-1/2ln(m)

is the same as

ln(v)=ln(sqrt(T/m))

is the same as

v=sqrt(T/m), m=T/v*v.

So, if [T]=N, [v]=m/s, you can easily extract [m]. And it is not m/s.