Three Pulleys 3 masses, find tension

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Homework Help Overview

The problem involves three masses (m1, m2, and m3) suspended from three massless and frictionless pulleys. The objective is to find the tension in the string when the system is in motion, with given masses of 6 kg, 2 kg, and 3 kg.

Discussion Character

  • Exploratory, Mathematical reasoning, Assumption checking

Approaches and Questions Raised

  • Participants discuss the equations of motion for the masses and attempt to relate them to find the tension. There are questions about the correctness of the equations and the resulting tension value.

Discussion Status

Some participants have confirmed the equations used are correct but have noted discrepancies in the calculated tension value. There is an acknowledgment of a potential misunderstanding regarding the expected answer options.

Contextual Notes

Participants are working with an old exam question and are trying to reconcile their results with provided answer options, which may not align with their calculations.

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Homework Statement



Three objects mI. m2 and m3 are suspended
from three massless and frictionless pulleys as
shown in the diagram. ml is 6 kg, m2 is 2 kg
and m3 is 3 kg. Find the tension of the string
when the system is set in motion (i.e. all
masses are moving). Answer in N

Options are:
(a) 11.3 (b) 12.1 (c) 13.5 (d) 14.2

..O...O... Top 2 pulleys attached to ceiling, m1 hangs from 1st pulley, m2 is attached
.| |..| |... to the middle pulley, m3 hangs from third pulley.
.|..O...|
.|..[]..|
[] m2 []
m1...m3

Homework Equations


Fg=mg
F=ma

The Attempt at a Solution



I made 3 equations, tried to relate them but I am getting 15.68N instead of any of the options (this was an old exam question). It's too far from 14.2 to be right. Here were the four equations I made:

a1=(m1g-T)/m1
a2=(2T-m2g)/m2
a3=(m3g-T)/m3

2a2=a1+a3

I keep getting none of the possible answers but I think I'm doing it right. Where did I go wrong?
 
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Your equations are right but your answer is wrong. Please post your working.
 
a1=(m1g-T)/m1=g-T/m1=g-T/3
a2=(2T-m2g)/m2=2T/m2-g=T-g
a3=(m3g-T)/m3=g-T/m3=g-T/6


From 4th eqn:

2T-2g=g-T/3+g-T/6

2T+T/2=4g

5T/2=4(9.8)

T=15.68
 
Oh, sorry, I misread the end of your first post. I thought you were getting 14.2. So, I agree with you, it's something around 16.
 
k thanks
 

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