Physics Fundamentals : Free Body Diagram

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Homework Help Overview

The discussion revolves around a physics problem involving a 5.0 kg mass suspended from the ceiling, with a horizontal force applied to maintain the string's position. Participants explore the forces acting on the mass, including gravity and tensions in the string, while attempting to determine the reading of the force on a spring balance using a scale diagram.

Discussion Character

  • Exploratory, Assumption checking, Conceptual clarification

Approaches and Questions Raised

  • Participants discuss the identification of forces acting on the mass, including gravity and tensions. There are questions about the correct application of trigonometric functions to relate the forces, particularly regarding the angles and components of tension. Some participants express confusion about the relationships between the forces and the setup of the problem.

Discussion Status

The discussion includes attempts to clarify misunderstandings about the forces involved and their components. Some participants have provided hints and guidance regarding the use of force vectors and the implications of the angles involved. There is an ongoing exploration of the relationships between the forces, but no explicit consensus has been reached.

Contextual Notes

Participants are working within the constraints of a homework assignment, which may limit the information available for solving the problem. There is a focus on understanding the setup and the forces at play without providing direct solutions.

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Homework Statement


A 5.0kg mass is suspended from the ceiling. A horizontal force F is applied to hold the string in position as shown

http://i.imgur.com/ZdR72ff.jpg

Determine the reading of F on the spring balance by using a scale diagram

Homework Equations



None

The Attempt at a Solution



http://i.imgur.com/2KO2AnT.jpg
Am I doing it correctly?
It doesn't really make sense to me. I can't determine the force F. I only have 30degree angle and the weight.
I don't know how to draw the length of Force F. What is it should I be looking for?

Thank you!
 
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Have you studied force vectors?
 
learn2physics said:

Homework Statement


A 5.0kg mass is suspended from the ceiling. A horizontal force F is applied to hold the string in position as shown

http://i.imgur.com/ZdR72ff.jpg

Determine the reading of F on the spring balance by using a scale diagram

Homework Equations



None

The Attempt at a Solution



http://i.imgur.com/2KO2AnT.jpg
Am I doing it correctly?
No.

It doesn't really make sense to me. I can't determine the force F. I only have 30degree angle and the weight.
I don't know how to draw the length of Force F. What is it should I be looking for?
1. What are all the forces are on the 5.0 kg. mass? Hint: I can see two tensions and gravity. Are there any others?

2. Draw force vectors for each force. hint: You have to work out the magnitude of the tensions, so put a "?" for them for now. You can determine the force and direction of gravity.

3. What do the forces all sum to? (hint: is there any acceleration here?).

4. Work out the magnitidue of the unknown forces.

AM
 
phinds said:
Have you studied force vectors?

I have look through my textbook and for this question I am having weird answers. I believd I have not fully understand yet.


Andrew Mason said:
No.


1. What are all the forces are on the 5.0 kg. mass? Hint: I can see two tensions and gravity. Are there any others?

2. Draw force vectors for each force. hint: You have to work out the magnitude of the tensions, so put a "?" for them for now. You can determine the force and direction of gravity.

3. What do the forces all sum to? (hint: is there any acceleration here?).

4. Work out the magnitidue of the unknown forces.

AM

I have tried to identify all the forces.

http://i.imgur.com/HexCRVQ.jpg

Does this make sense? I made a bad calculation mistake on previous attempt
From what I understand, mass will exert a weight of 50N. Therefore the tension at T1 will be 50N. Tension at T2 will also be 50N because the weight is pulling it down. The resultant force has to be 0 as it is stationary. The force on the weight and tension will cancel out each other. I am now left with Force F. I can't go anywhere from here. Which part am I getting it wrongly?

Thank you!
 
learn2physics said:
From what I understand, mass will exert a weight of 50N. Therefore the tension at T1 will be 50N.
Good.

Tension at T2 will also be 50N because the weight is pulling it down.
No. Realize that T2 acts at an angle.

The resultant force has to be 0 as it is stationary. The force on the weight and tension will cancel out each other. I am now left with Force F. I can't go anywhere from here. Which part am I getting it wrongly?
T2 does not cancel the weight. But the vertical component of T2 does.
 
Doc Al said:
Good.


No. Realize that T2 acts at an angle.


T2 does not cancel the weight. But the vertical component of T2 does.

OH!
If I am understanding it correctly,
The vertical component of T2 is 50N
Therefore force F is at the base.

http://i.imgur.com/NCCD8Hy.jpg

Am I right to say:
Using a scale diagram, 1cm representing 10N


sin(30) = F/5
F = 5sin(30)
F= 2.5cm

Therefore, the reading of force F is 25N.

Am I understanding it correctly?

Thank you!
 
learn2physics said:
sin(30) = F/5
F = 5sin(30)
F= 2.5cm

Why did you say sin(30°) = \frac{F}{5} ? Wouldn't it be sin(30°) = \frac{F}{T_2}
("sine = opposite / hypotenuse")
 
Nathanael said:
Why did you say sin(30°) = \frac{F}{5} ?


Wouldn't it be sin(30°) = \frac{F}{T_2}



("sine = opposite / hypotenuse")

Oh my! Sorry! What a silly mistake I made.

It should be
tan(30) = F/5 (opposite/adjacent)
F = 5tan(30)
F = 2.89 (3 sig. fig.)

Therefore the force F is 28.9N

Am I understanding this correctly?

Thank you!
 
learn2physics said:
Oh my! Sorry! What a silly mistake I made.

It should be
tan(30) = F/5 (opposite/adjacent)
F = 5tan(30)
F = 2.89 (3 sig. fig.)

Therefore the force F is 28.9N

Am I understanding this correctly?

Thank you!

Yes I think that is correct.
 
  • #10
Nathanael said:
Yes I think that is correct.

Thank you very much for your help!

So my mistake was not recognising the vertical component of T2.

Thank you!
 

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