# Homework Help: Wave in a string question

1. Aug 12, 2008

### kidsmoker

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

"A uniform rope with length L and mass m is held at one end and whirled in a horizontal circle with angular velocity w. You can ignore the force of gravity on the rope. Find the time required for a transerve wave to travel from one end of the rope to the other."

2. Relevant equations

w = 2*pi*f
wave speed = frequency*wavelength = sqrt(tension/mass per unit length)

3. The attempt at a solution

I'm a bit confused here. If the force of gravity on the rope is being ignored, then what is the tension in the rope?

2. Aug 12, 2008

### alphysicist

Hi kidsmoker,

Think about what has to be true for the mass to travel in a circular path.

3. Aug 12, 2008

### kidsmoker

There's a force mw^2A acting towards the centre? Do I take this as the tension in the string? I'm still not sure what to do sorry...

Last edited: Aug 12, 2008
4. Aug 12, 2008

### LowlyPion

What is "A" in your equation?

5. Aug 12, 2008

### kidsmoker

Sorry, the radius of the circular motion. I called it A cos it's like the amplitude.

6. Aug 12, 2008

### LowlyPion

In your problem that is actually "L" and yes that is the centripetal force on the string which is your Tension that you are looking for.

7. Aug 12, 2008

### kidsmoker

Are you sure? Why would it be equal to the length of the string?

8. Aug 12, 2008

### LowlyPion

Perhaps this will help?
http://hyperphysics.phy-astr.gsu.edu/hbase/cf.html#cf

Wait a minute is there a mass at the end of the rope or is the rope itself mass M total?

Maybe I am misreading the problem?

Last edited: Aug 12, 2008
9. Aug 27, 2008

### kidsmoker

I ws completely misreading the question too. I thought that the string was hanging vertically and you were whirling the top end in a circle, so that these circular waves travel down the string. I realise now that it means that the whole string is horizontal and it's being whirled in a circle like this, so as to keep it taut. In that case the problem is easy :P

Thanks anyway!