geerky42
  • geerky42
In this system, how can you determine which direction it will rotate?
Physics
  • Stacey Warren - Expert brainly.com
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SOLVED
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schrodinger
  • schrodinger
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geerky42
  • geerky42
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geerky42
  • geerky42
Like, if \(m_1\) is larger than \(m_2\), how can you tell which way it will rotate?
geerky42
  • geerky42
Sorry for keeping asking you for help, but can you answer this question, @shubhamsrg ?

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shubhamsrg
  • shubhamsrg
Product of mr will decide that
geerky42
  • geerky42
Why does it work?
shubhamsrg
  • shubhamsrg
Clockwise torque = (m2)g(r2) ANti clockwise torque = (m1)g(r1) Greater torque will prevail
geerky42
  • geerky42
I'm confused...
shubhamsrg
  • shubhamsrg
Also, am assuming its a massless pulley , right ?
geerky42
  • geerky42
Well, the problem I'm currently working on, it doesn't say anything about the mass of pulley... but it does say that the combined moment of inertia of the two wheels is 2.7 kg·m². So pulley or wheels has mass?
shubhamsrg
  • shubhamsrg
Yes pulleys has mass.
geerky42
  • geerky42
Here's the problem.
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shubhamsrg
  • shubhamsrg
Be right back.
geerky42
  • geerky42
The reason I ask this question is because I want to set up a sum of force for both two masses correctly and I don't know which to go first; mg or T (tension)
geerky42
  • geerky42
If mass goes upward, T goes first, otherwise, m·g goes first.
geerky42
  • geerky42
My attempt is to set up some equations then do some substitution and isolate and find \(\alpha\) in term of variables that already have given value. I don't know if this can work.
shubhamsrg
  • shubhamsrg
Okay am back
shubhamsrg
  • shubhamsrg
Well simply write eqn of rotation.
geerky42
  • geerky42
\(\sum \tau = T_1R_1 - T_2 R_2 = I\alpha\) OR \(\sum \tau = T_2R_2 - T_1 R_1 = I\alpha\) It depends which direction it rotates... I also need to find two tensions...
geerky42
  • geerky42
\[\sum F_1 = m_1g - T_1 = m_1 a\] OR \[\sum F_1 = T_1 - m_1g = m_1 a\] \[\sum F_2 = m_2g - T_2 = m_2 a\] OR \[\sum F_2 = T_2 - m_2g = m_2 a\] That's why I need to determine which direction it rotates...
geerky42
  • geerky42
Any ideas? "Clockwise torque = (m2)g(r2) ANti clockwise torque = (m1)g(r1) Greater torque will prevail" This works only if pulley is massless, right?
shubhamsrg
  • shubhamsrg
You can take any direction to be +ve. If your assumption would be wrong, it'll automatically come to be -ve
geerky42
  • geerky42
Ugh, I hope I make right guess first, lol.
geerky42
  • geerky42
What is ve?
shubhamsrg
  • shubhamsrg
negatiVE
geerky42
  • geerky42
What is angular acceleration is negative? How can I know if my assumption is right or wrong?
geerky42
  • geerky42
Problem asks me to "take clockwise direction as positive."
geerky42
  • geerky42
Wait, angular acceleration cannot be negative, right?
shubhamsrg
  • shubhamsrg
It is a vector, it can be negavtive, -ve will just denote the direction.
shubhamsrg
  • shubhamsrg
The linear acceleration of both masses will not be equal
shubhamsrg
  • shubhamsrg
m1g - T1 = m1 a1 T2 - m2g = m2 a2 T1 r1 - T2 r2 = I alpha
geerky42
  • geerky42
Is it possible to find angular acceleration in this way?
shubhamsrg
  • shubhamsrg
I am getting confused. @Vincent-Lyon.Fr
geerky42
  • geerky42
It seems like there is too much unknown variables.
geerky42
  • geerky42
lol, me too...
geerky42
  • geerky42
@hartnn @JamesJ @saifoo.khan Can you help me?
geerky42
  • geerky42
@zepdrix @AccessDenied
geerky42
  • geerky42
Apparently I'm not going to get any help for long time.
anonymous
  • anonymous
You don't have to know the direction of rotation of the pulley before you solve the equations. You just take one of the directions as positive and the other one as negative. This choice is completely arbitrary (But since the given problem asks you to take the clockwise direction as positive, you just go ahead with that). After you solve the problem, if the end up with positive angular acceleration, it's in the direction that you chose (In this case, clockwise). If it turns out to be negative, it's in the opposite direction (In this case, counter-clockwise).
Vincent-Lyon.Fr
  • Vincent-Lyon.Fr
Quote : "Clockwise torque = (m2)g(r2) ANti clockwise torque = (m1)g(r1) Greater torque will prevail" This works only if pulley is massless, right? No, this works whatever the moment of inertia of the pulley. It is a good idea to anticipate the direction of motion this way.
geerky42
  • geerky42
It makes sense. Thanks, everybody!

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