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geerky42 Group Title

In this system, how can you determine which direction it will rotate?

  • one year ago
  • one year ago

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  1. geerky42 Group Title
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    • one year ago
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  2. geerky42 Group Title
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    Like, if \(m_1\) is larger than \(m_2\), how can you tell which way it will rotate?

    • one year ago
  3. geerky42 Group Title
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    Sorry for keeping asking you for help, but can you answer this question, @shubhamsrg ?

    • one year ago
  4. shubhamsrg Group Title
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    Product of mr will decide that

    • one year ago
  5. geerky42 Group Title
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    Why does it work?

    • one year ago
  6. shubhamsrg Group Title
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    Clockwise torque = (m2)g(r2) ANti clockwise torque = (m1)g(r1) Greater torque will prevail

    • one year ago
  7. geerky42 Group Title
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    I'm confused...

    • one year ago
  8. shubhamsrg Group Title
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    Also, am assuming its a massless pulley , right ?

    • one year ago
  9. geerky42 Group Title
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    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?

    • one year ago
  10. shubhamsrg Group Title
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    Yes pulleys has mass.

    • one year ago
  11. geerky42 Group Title
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    Here's the problem.

    • one year ago
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  12. shubhamsrg Group Title
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    Be right back.

    • one year ago
  13. geerky42 Group Title
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    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)

    • one year ago
  14. geerky42 Group Title
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    If mass goes upward, T goes first, otherwise, m·g goes first.

    • one year ago
  15. geerky42 Group Title
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    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.

    • one year ago
  16. shubhamsrg Group Title
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    Okay am back

    • one year ago
  17. shubhamsrg Group Title
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    Well simply write eqn of rotation.

    • one year ago
  18. geerky42 Group Title
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    \(\sum \tau = T_1R_1 - T_2 R_2 = I\alpha\) 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...

    • one year ago
  19. geerky42 Group Title
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    \[\sum F_1 = m_1g - T_1 = m_1 a\] 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...

    • one year ago
  20. geerky42 Group Title
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    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?

    • one year ago
  21. shubhamsrg Group Title
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    You can take any direction to be +ve. If your assumption would be wrong, it'll automatically come to be -ve

    • one year ago
  22. geerky42 Group Title
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    Ugh, I hope I make right guess first, lol.

    • one year ago
  23. geerky42 Group Title
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    What is ve?

    • one year ago
  24. shubhamsrg Group Title
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    negatiVE

    • one year ago
  25. geerky42 Group Title
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    What is angular acceleration is negative? How can I know if my assumption is right or wrong?

    • one year ago
  26. geerky42 Group Title
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    Problem asks me to "take clockwise direction as positive."

    • one year ago
  27. geerky42 Group Title
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    Wait, angular acceleration cannot be negative, right?

    • one year ago
  28. shubhamsrg Group Title
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    It is a vector, it can be negavtive, -ve will just denote the direction.

    • one year ago
  29. shubhamsrg Group Title
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    The linear acceleration of both masses will not be equal

    • one year ago
  30. shubhamsrg Group Title
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    m1g - T1 = m1 a1 T2 - m2g = m2 a2 T1 r1 - T2 r2 = I alpha

    • one year ago
  31. geerky42 Group Title
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    Is it possible to find angular acceleration in this way?

    • one year ago
  32. shubhamsrg Group Title
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    I am getting confused. @Vincent-Lyon.Fr

    • one year ago
  33. geerky42 Group Title
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    It seems like there is too much unknown variables.

    • one year ago
  34. geerky42 Group Title
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    lol, me too...

    • one year ago
  35. geerky42 Group Title
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    @hartnn @JamesJ @saifoo.khan Can you help me?

    • one year ago
  36. geerky42 Group Title
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    @zepdrix @AccessDenied

    • one year ago
  37. geerky42 Group Title
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    Apparently I'm not going to get any help for long time.

    • one year ago
  38. rajathsbhat Group Title
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    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).

    • one year ago
  39. Vincent-Lyon.Fr Group Title
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    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.

    • one year ago
  40. geerky42 Group Title
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    It makes sense. Thanks, everybody!

    • one year ago
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