How Do You Calculate Torque to Determine String Tension in Physics Problems?

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Homework Help Overview

The discussion revolves around calculating torque to determine string tension in a physics problem involving a mass placed on a board supported by strings. Participants are exploring the relationship between the position of the mass and the resulting tension in the strings.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • Participants discuss the placement of the mass and its effect on string tension, with one participant attempting to calculate the tension as a function of distance 'x' from a reference point. Questions arise about the implications of the calculated distance and the conditions under which the strings might break.

Discussion Status

There is an ongoing exploration of the implications of the calculated distance for the mass and how it relates to the stability of the strings. Some participants have provided guidance on interpreting the results and translating them into the required format, while others are questioning the assumptions made in the calculations.

Contextual Notes

Participants are working within the constraints of a homework assignment, which may limit the information available and the methods allowed for solving the problem. There is a focus on understanding the physical setup and the consequences of different placements of the mass on the board.

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Homework Statement



I am stuck on question 6c on this paper. Can anyone have a look at it please. I don't know were to start.

do I place the rock 'x' meters away from one of the strings and set one of the strings tension to 40g?

Homework Equations


The Attempt at a Solution

 

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Yes, that will work.

Find the tension in the strings as a function of 'x'.
 
Doc Al said:
Yes, that will work.

Find the tension in the strings as a function of 'x'.

Okay I have done this, but I don't get the right answer.

heres my working,

taking moments about A (490 \times 4) + (196 \times x) = 392 \times 8

1960 + 196x = 3136

196x = 1176

x = 6

is my diagram correct?
http://www.mathhelpforum.com/math-help/attachments/advanced-applied-math/9244d1229179227-mechanics-help-untitled.jpg

the right answer is \frac{1}{2}
 
Last edited by a moderator:
Your work and diagram are perfectly correct. You just need to translate your answer into the form that they want. They asked for the fraction of the board, not the position of the mass. :wink:
 
Doc Al said:
Your work and diagram are perfectly correct. You just need to translate your answer into the form that they want. They asked for the fraction of the board, not the position of the mass. :wink:

I don't know how to work that out...
 
What does your answer (x = 6) mean? What happens for x > 6? You did torques about point A, what if you did the same thing about point B?

(Hint: In your diagram, mark each portion of the board where placing the mass would lead to a string breaking.)
 
Doc Al said:
What does your answer (x = 6) mean? What happens for x > 6? You did torques about point A, what if you did the same thing about point B?

(Hint: In your diagram, mark each portion of the board where placing the mass would lead to a string breaking.)

x=6 means the distance the weight of the rock acts from point A?

if x is greater than 6 than one of the strings will break right?
 
tweety1234 said:
x=6 means the distance the weight of the rock acts from point A?

if x is greater than 6 than one of the strings will break right?
Right. So how much of the board is "off limits" for the string not to break? (Consider both ends.)
 
doc al said:
right. So how much of the board is "off limits" for the string not to break? (consider both ends.)

8-6=2?
 
  • #10
tweety1234 said:
8-6=2?
Yes, viewed from side A. Now view from the other side.
 
  • #11
Doc Al said:
Yes, viewed from side A. Now view from the other side.

it would be the same wouldn't it?

I don't think I am going to ever understand this hehe

so thanks for you help!

edit: is it 4?
 
  • #12
tweety1234 said:
it would be the same wouldn't it?
That's right.

edit: is it 4?
Yes. Analzying things form side A tells you that placing the mass between 6 and 8 meters from A will cause string B to break. A similar analysis applies from side B. That means 2 m on both ends of the board are off limits--a total of 4 m out of 8. What fraction is that? :wink:
 
  • #13
Doc Al said:
That's right.


Yes. Analzying things form side A tells you that placing the mass between 6 and 8 meters from A will cause string B to break. A similar analysis applies from side B. That means 2 m on both ends of the board are off limits--a total of 4 m out of 8. What fraction is that? :wink:

OH MY GOD I GET IT NOW!

thanks for patiently helping me
 

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