What is the length of the string?

[ThePhysicsXV]

Homework Statement

A wave along a 15 gram string travels at 756 m/s when it is tightened to 189N?

Homework Equations

V = sqr root T/ m/l

The Attempt at a Solution

[/B]
I got 3.30 x 10^-4

 

[berkeman]

Homework Statement

A wave along a 15 gram string travels at 756 m/s when it is tightened to 189N?

Homework Equations

V = sqr root T/ m/l

The Attempt at a Solution

[/B]
I got 3.30 x 10^-4

Welcome to the PF.

That looks kind of small for a length of string... What are the units?

Can you show your work (including units) to solve the equation for the length?

 

[Guneykan Ozgul]

Your result seems the mass per unit length not length.

 

[ThePhysicsXV]

Your result seems the mass per unit length not length.

I'm confuse, so what's the correct formula or way to solving for the length?

 

[berkeman]

I'm confuse, so what's the correct formula or way to solving for the length?

It looks like you wrote the correct equation, but the quantity in the denominator is the mass per unit length...

http://hyperphysics.phy-astr.gsu.edu/hbase/waves/string.html

 

[Guneykan Ozgul]

Well, you already knew the formula to calculate the m/L (assuming string is uniform).So you can calculate mass per unit length(m/L) by just puttin v and T into equation. Then you can find L using mass(15 g).

 

[ThePhysicsXV]

Well, you already knew the formula to calculate the m/L (assuming string is uniform).So you can calculate mass per unit length(m/L) by just puttin v and T into equation. Then you can find L using mass(15 g).

So mass is gram or I have to do it on kg

 

[Guneykan Ozgul]

So mass is gram or I have to do it on kg

You should first convert it to kg to be able to express length in meters. If you use gram you find length in terms of centimeters.

 

[ThePhysicsXV]

You should first convert it to kg to be able to express length in meters. If you use gram you find length in terms of centimeters.

So what's the correct formula?

 

[berkeman]

So what's the correct formula?

You already wrote it in Post #1.

Just re-arrange it to isolate the length on the lefthand side (LHS) of the equation, and substitute the numbers that you have been given in the problem statement. Be sure to convert to mks units as appropriate.

Please show us your work, and your final solution so that we can check it.

 

[Guneykan Ozgul]

I got << Deleted by Mentor >> if no mistake. You should use kg or g depending on your preference to express length.

 

[ThePhysicsXV]

I got L=m/(T/v^2) if no mistake. You should use kg or g depending on your preference to express length.

I got 4.96x10^-6 am I correct?

 

[berkeman]

I got << Deleted by Mentor >> if no mistake. You should use kg or g depending on your preference to express length.

Please don't do the student's work for them. That's one of the HH rules. He's almost got it figured out on his own now...

 

[berkeman]

I got 4.96x10^-6 am I correct?

Almost certainly not. That length is in meters? Please show your detailed work, including units in your equations.

 

[ThePhysicsXV]

Almost certainly not. That length is in meters? Please show your detailed work, including units in your equations.

L= .015m(189N/756m/s ^2)

 

[berkeman]

.015m

What's that?

/756m/s ^2

Please use better parenthesis to show what is getting squared and what all the units are...

 

[berkeman]

I got 4.96x10^-6 am I correct?

I think I see where your error is.

You get that answer if you use the incorrect formula v = \sqrt{\frac{T}{\frac{L}{m}}}

Instead of the correct formula that you listed in Post #1 and is in my Hyperphysics link: v = \sqrt{\frac{T}{\frac{m}{L}}}

 

[ThePhysicsXV]

I think I see where your error is.

You get that answer if you use the incorrect formula v = \sqrt{\frac{T}{\frac{L}{m}}}

Instead of the correct formula that you listed in Post #1 and is in my Hyperphysics link: v = \sqrt{\frac{T}{\frac{m}{L}}}

I got L = (mv^2)/T

 

[berkeman]

I got L = (mv^2)/T

Good. Now plug in the numbers you were given (and show units in square brackets [] or similar to make sure the units of the final answer are right), and solve!

 

[ThePhysicsXV]

Good. Now plug in the numbers you were given (and show units in square brackets [] or similar to make sure the units of the final answer are right), and solve!

L= (.015m*756m/s ^2)/(189)
L= 45.36 m

 

[berkeman]

L= (.015m*756m/s ^2)/(189)
L= 45.36 m

Bingo!

 

[ThePhysicsXV]

Bingo!

You sir is the best! Thanks I still have more questions to ask. Related to Waves and Sounds, should I do another post?

 

[berkeman]

You sir is the best! Thanks

Hey, it was teamwork with @Guneykan Ozgul

I still have more questions to ask. Related to Waves and Sounds, should I do another post?

Yes please. A new question would go in its own new thread.