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

In summary, the conversation discusses the calculation of tension (T) in a system with a constant velocity. The equation P=T+25 N and P+T=125 are both considered, with the conclusion that T always pulls away from the object. The direction of T for a 100 N weight and a 25 N weight is discussed, and a free body diagram is suggested to help visualize the concept. A question about T=100N is raised and it is determined that P=125. The conversation ends with the confirmation that P=125 and T=100N.
  • #1
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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  • #2
Which direction does T pull on the 100 N weight?
Which direction does T pull on the 25 N weight?
 
  • #3
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
 
  • #4
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?
 
  • #5
Perhaps draw a two free body diagrams, one for each mass.
 
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  • #6
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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  • #7
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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  • #8
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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What is tension in a string?

Tension in a string is the force that is applied to the string, causing it to stretch or elongate. It is a result of the pulling or stretching forces acting on the string from opposite ends.

What is the difference between P=T+25 N and P+T=125?

P=T+25 N and P+T=125 are two different ways of representing the same equation, which is the equation for tension in a string. The first equation states that the tension in the string (T) is equal to the applied force (P) plus an additional 25 Newtons. The second equation states that the sum of the applied force (P) and the tension in the string (T) is equal to 125 Newtons.

How is tension in a string calculated?

Tension in a string is calculated using the formula T = F*l, where T is tension, F is the applied force, and l is the length of the string. This formula assumes that the string is in equilibrium, meaning that the forces acting on it are balanced.

What factors affect tension in a string?

The tension in a string is affected by several factors, including the strength of the string, the amount of force applied to it, and the length of the string. Other factors that may affect tension include the type of material the string is made of and any external forces acting on the string, such as wind or gravity.

Why is understanding tension in a string important in science?

Understanding tension in a string is important in science because it is a fundamental concept in mechanics and is often used in experiments and calculations. It is also important in engineering and design, as it helps in determining the strength and stability of structures that involve strings, such as bridges or suspension systems.

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