# Homework Help: Tension in a rope, wavelengths, etc. I need help!

1. Dec 5, 2011

### somesmallkid

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

A rope is stretched between two vertical supports. The points where it is attached (P and Q) are fixed. The linear density of the rope, u, is 0.6kg/m, and the speed of the transverse waves on the rope is 12 m/s.

a. what is the tension in the rope?
b. with what frequency must the rope vibrate to create a traveling wave with a wave length of 4m?

The rope can support standing waves of lengths 4m and 3.2m, whose harmonic numbers are consecutive integers.

c. find the length of the rope
d. find the mass of the rope
e. what is the harmonic number of the 4m standing wave?

2. Relevant equations

f=1/T
T=2pi(m/k)^1/2
=2pi(L/g)^1/2
v=(wavelength)f
F(t)=u(v)^2
f=v/wavelength
2L/n=4m
2L/(n+1)=3.2m

3. The attempt at a solution

a. (0.4 kg/m)(12m/s)^2= 58N

b. f = (12m/s)/(2m) = 6 Hz

c. n=4

2L = 16 for both
L=8m

Last edited: Dec 5, 2011
2. Dec 5, 2011

### grzz

u = 0.6kg/m or 0.4kg/m?

3. Dec 5, 2011

### somesmallkid

Oh, it's 0.6kg/m. Sorry it's kind of late and I guess I'm just tired of trying to solve this problem :I hehe..

4. Dec 5, 2011

### grzz

Is not the wavelength 4m?

5. Dec 5, 2011

### somesmallkid

No, you're right. It's 4.

6. Dec 5, 2011

### somesmallkid

Am I doing these correctly?

7. Dec 5, 2011

### grzz

Length of rope = 8m

8. Dec 5, 2011

### somesmallkid

yeah i got that :) thanks! do you know how to do D or E though?

9. Dec 5, 2011

### grzz

re D
Your post says,'...The linear density of the rope, u, is 0.6kg/m,...' and you know the length of rope.

re E

What do you understand by 'fundamental frequency'?