A Question About Pulleys and Spring Scales

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Homework Help Overview

The problem involves two 5 kg masses hanging from pulleys on opposite ends of a table, with a focus on determining the reading of a spring scale positioned in the middle of a massless string connecting the masses. The setup includes assumptions of a massless string and frictionless pulleys.

Discussion Character

  • Exploratory, Assumption checking

Approaches and Questions Raised

  • Participants discuss the calculation of the spring scale reading, with initial attempts yielding 49N and questions about whether the reading should be 98N due to both masses being equal. There is also confusion regarding the units of the answer, with some participants questioning the interpretation of the scale reading in terms of mass versus force.

Discussion Status

Participants are exploring different interpretations of the problem, particularly regarding the correct units for the spring scale reading. Some guidance has been provided regarding the relationship between force and mass, but no consensus has been reached on the final answer.

Contextual Notes

There is a noted confusion about the expected units for the spring scale reading, as some participants initially calculate the force in Newtons while others clarify that the answer should be expressed in kilograms.

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Homework Statement


The question shows two 5kg masses at rest hanging from two pulleys on opposite ends of a table. The string is massless and the pulley is frictionless.


Homework Equations


They want to know what the spring scale reads (in the middle of the masslessstring).

The Attempt at a Solution


This is what I thought:

Fspring= w=mg
5kg*9.8m/s^2= 49N
This answer was wrong.

Would the answer be 98N since both masses are the same?
 
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mcnealymt said:
They want to know what the spring scale reads (in the middle of the masslessstring).
Assuming I understand the setup, the spring scale will read the tension in the string.

Fspring= w=mg
5kg*9.8m/s^2= 49N
This answer was wrong.
I'd say that answer was correct. Why do you think it's wrong?

Would the answer be 98N since both masses are the same?
No.
 
I must be going crazy . What about the mass of the system? Wouldn't it be 10?
 
Last edited:
mcnealymt said:
What about the mass of the system? Wouldn't it be 10?
If by "system" you mean both 5 kg masses together, then sure.

What are the exact questions you are being asked?
 
The string is massless and the pulley is frictionless. The spring sclae reads in kg. What is the reading of the scale?
 
mcnealymt said:
The spring sclae reads in kg.
There's the problem: They want the answer in kg, not Newtons.
 
So wouldn't the answer just be five because 49N is 5kg.
 
  • #10
mcnealymt said:
So wouldn't the answer just be five because 49N is 5kg.
Yes, the answer will be 5 kg.
 
  • #11
Thank you Doc Al. I highly appreciate it.
 

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