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Tricky question involving masses, a pulley on incline with friction

  • #26
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Oh!!! I understand now. The force of friction (static) shouldn't oppose each other, because I want to find out the mass it would take just so it would move (up or down) the incline.
Yep you got it. Your FBD and math looks right so your answer should be right. Although your answer would actually be m2<1.24.
 
  • #27
SammyS
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There should be two limiting values for m2.

If m2 is very small, then the system will accelerate toward the right. This results in an answer such as m2 < msmall. This is the case you have solved, m2 < 1.24 kg.

If m2 is very large, then the system will accelerate toward the left. This results in an answer such as m2 > mlarge.
 
  • #28
Yep you got it. Your FBD and math looks right so your answer should be right. Although your answer would actually be m2<1.24.
My Physics teacher went through this today and 1.24kg is right but that is the weight when it is about to move up. But there should also be another weight that is the heavier one that just makes it go down.

Gah, I knew right at the beginning before I even started that there should be two masses! Well, I did find one. The other one (the heavier) turned out to be 4.9 something (close to 5kg) can't remember. I did get it at one point when I tried out possible ways to tackle this question.
 

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