Atwood with Sliding mass and real pulley

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Homework Help Overview

The problem involves an Atwood machine with a sliding mass and a real pulley. It presents a scenario where one block is on a horizontal surface while another block hangs vertically, and the task is to calculate the speed of the hanging block after it falls a certain distance, as well as the angular speed of the pulley at that moment.

Discussion Character

  • Mixed

Approaches and Questions Raised

  • Participants discuss the relationship between the tensions acting on the pulley and the accelerations of the blocks, questioning whether they are the same. There is also mention of using conservation of energy as a potential approach to solve the problem.

Discussion Status

Some participants have offered guidance on considering conservation of energy as a method for solving the problem. There is ongoing exploration of the assumptions regarding the pulley’s friction and the nature of the forces involved.

Contextual Notes

Participants note that all relevant information is provided within the problem statement, and there is uncertainty about whether the pulley is frictionless, which may affect the analysis.

SadDan
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Homework Statement


Block 1 with mass m1=4.04 kg rests on a very low friction horizontal ledge. This block is attached to a string that passes over a pulley, and the other end of the string is attached to the hanging block 2 of mass m2=2.02 kg, as shown.

The pulley is a uniform disk of radius 11.85 cm and mass 1.980 kg. Calculate the speed of block 2 after it is released from rest and falls a distance of 1.84 m.

What is the angular speed of the pulley at the instant when block 2 has fallen a distance of 1.84 m ?

Homework Equations


Wtot=change in Energy
KE=1/2 mv^2
W=integral of force*displacement
N2L for rotation and translation

The Attempt at a Solution


The tension of 2 and 1 on the pulley should be different but the accelerations of the blocks would be the same?
a=m2*g/(mp/2 +m1+m2)
T2=m2(g-a)=13.27
T1=m1*a=13.0829
WEm2=integral from 0 to 1.84 (T2xdx) = 22.47 J
WT1m1=integral from 0 to 1.84 (T1xdx) = 22.1467 J
work energy theorem:
KE=W
1/2mv^2=WEm2+WT1m1
v=sqrt(2(WEm2+WT1m1)/mp)=3.33m/s

This is not the correct answer, I'm not sure what I am doing wrong would the energy side of the equation be only kinetic?
 
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I think the diagram would be helpful. Is the pulley frictionless? Also why would the accelerations be same?
 
m1 and m2 are atached by a string on a pulley so wouldn't their accelerations be the same?
Screen Shot 2017-04-03 at 12.21.06 AM.png
 
And all the information we were given is on the question so I'm assuming its not frictionless
 
SadDan said:
m1 and m2 are atached by a string on a pulley so wouldn't their accelerations be the same?

Correct. I can't really understand what the equations for work you've written, up you can just use conservation of energy to do the problem.
 

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