Tension in a String: Explaining P=T+25 N vs P+T=125

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Homework Help Overview

The discussion revolves around the tension in a string system involving two weights, one of 100 N and another of 25 N. Participants are exploring the relationships between the forces acting on these weights and the equations that describe them.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • Participants are attempting to clarify the correct relationship between the forces, questioning why one equation (P=T+25 N) is preferred over another (P+T=125 N). There are discussions about the direction of tension and its effects on the weights involved.

Discussion Status

Some participants have offered insights into drawing free body diagrams to visualize the forces, which has led to differing interpretations of the equations. There is an ongoing exploration of the implications of these diagrams on the relationships between P, T, and the weights.

Contextual Notes

Participants are working under the assumption that the system is in constant velocity, leading to a net force of zero. There is also a mention of the weight (W) being equal to tension (T) in one of the diagrams, which influences the calculations being discussed.

Lori

Homework Statement


upload_2017-11-4_22-13-46.png


Homework Equations



Ook, so I'm really bad at physics, and i need someone to help explain why the answer is P=T+25 N
I thought it is P+T = 125

The Attempt at a Solution



Since the system is in constant velocity, then Fnet = 0 so that P + T + W = 0 Why isn't it P + T + 125 =0?[/B]
 

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Which direction does T pull on the 100 N weight?
Which direction does T pull on the 25 N weight?
 
jbriggs444 said:
Which direction does T pull on the 100 N weight?
Which direction does T pull on the 25 N weight?
T always pull away from the object. So, for the 100 N weight, Tension pulls downward and for 25N, the tension pulls upward
 
Lori said:
T always pull away from the object.
Yes.
Lori said:
So, for the 100 N weight, Tension pulls downward ...
Away from the 100N weight would be upwards, surely?
 
Perhaps draw a two free body diagrams, one for each mass.
 
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CWatters said:
Perhaps draw a two free body diagrams, one for each mass.
Thanks , i drew it for the 25 N object and got that P = T+25!

upload_2017-11-5_12-26-26.png
 

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I have a question to add!
If i know that W = T for the second diagram , then I know that T = 100N right?

I can actually find P since P = 25+T , so that P=125
 
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Lori said:
If i know that W = T for the second diagram , then I know that T = 100N right?

I can actually find P since P = 25+T , so that P=125
Right!
 
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