[SOLVED] Same string, different mass per unit length, whats the wavelength?


by bobbo7410
Tags: length, mass, solved, string, unit, wavelength
bobbo7410
bobbo7410 is offline
#1
Feb4-08, 06:45 PM
P: 36
*oddly I can't edit the original title?

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

A string is made of two materials of different mass per unit length. On the left side of the string, the mpu is given as well as its wavelength. On the right only the mpu. The question asks for the right side's wavelength.

2. Relevant equations

xxx

3. The attempt at a solution

I immediately began doing just a simple balancing equations. 2.76/20.4 = 3.63X

yet it returned the answer as incorrect. How can that be??

as well, I thought maybe it was trick question since its all the same single string, the wavelength must be the same. so I put 20.4 and as well it returned it as incorrect.

I'm really not sure what I did wrong.
Phys.Org News Partner Science news on Phys.org
Better thermal-imaging lens from waste sulfur
Hackathon team's GoogolPlex gives Siri extra powers
Bright points in Sun's atmosphere mark patterns deep in its interior
Doc Al
Doc Al is offline
#2
Feb4-08, 07:05 PM
Mentor
Doc Al's Avatar
P: 40,877
How does the wavelength (or wave speed) depend on the mass per unit length?
bobbo7410
bobbo7410 is offline
#3
Feb4-08, 07:15 PM
P: 36
Not sure if you were questioning me or you stating the problem variables don't depend on one another.

mu (mpl or mass per unit length) = string mass / string length

v = square root of (T / mu) where t = mg

thats all I can really find or think of regarding mu

Doc Al
Doc Al is offline
#4
Feb4-08, 07:18 PM
Mentor
Doc Al's Avatar
P: 40,877

[SOLVED] Same string, different mass per unit length, whats the wavelength?


Quote Quote by bobbo7410 View Post
v = square root of (T / mu) where t = mg
Good. The square root is key. That's what you were missing earlier.
bobbo7410
bobbo7410 is offline
#5
Feb4-08, 07:31 PM
P: 36
? earlier all i had was a simply balanced equation thats it.

v = square root (T/mg) T being the period and mg being mass * gravity

I dont know T, or the mass.

perhaps you could break it down a little more basic for me.

Thanks for the help!
Doc Al
Doc Al is offline
#6
Feb4-08, 07:46 PM
Mentor
Doc Al's Avatar
P: 40,877
Quote Quote by bobbo7410 View Post
? earlier all i had was a simply balanced equation thats it.
Your balance equation was incorrect. Come up with a new one using the equation for wave speed.
v = square root (T/mg) T being the period and mg being mass * gravity
I thought we agreed that: v = square root (T/mu)
You don't need to know the tension, since it's the same for both sides of string.

Combine this with the "wave equation": v = f * wavelength. (Hint: The frequency is also the same for both sides.)
bobbo7410
bobbo7410 is offline
#7
Feb4-08, 08:02 PM
P: 36
: ) thank you! that made it much simpler for me, I got it correct.

for some reason I looked back and the mu looked like mg.

So basically:

v = square root (T / mu)
v = f * wavelength

so [ f * wavelength = square root ( T / mu ) ]

I set the frequency to 1 for both so I only had 1 variable to determine. I solved for T on the left side of the string and once I found that I used that same T to determine the wavelength for the right side.

yey thanks doc
bobbo7410
bobbo7410 is offline
#8
Feb4-08, 08:18 PM
P: 36
http://www.physicsforums.com/showthr...41#post1597041

for my first equation.. Would it be beneficial to use the same setup as above to solve for frequency or T?

because if I were to find either of those I could easily find the velocity. yet I think am back where I started (2 unknown variables) since I can't simply substitute 1 for the frequency in that problem.


Register to reply

Related Discussions
[SOLVED] [Multiple Choice] ...wavelength of an object. de Broglie wavelength Introductory Physics Homework 11
[SOLVED] Finding mass per unit length for stretched strng given tension? Introductory Physics Homework 1
Wavelength and length of wire limitation? General Physics 3
[SOLVED] Mass per Unit Length of Violin Strings Introductory Physics Homework 1
[SOLVED] how is it that the Atomic Mass Unit is less than either the General Physics 5