3 pulleys - 2 masses on incline plane

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Homework Help Overview

The discussion revolves around a physics problem involving three pulleys and two masses on an inclined plane. The original poster attempts to verify the conditions under which a log will move up the ramp, given specific parameters such as mass, friction, angle, and gravitational force.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • Participants explore the forces acting on the blocks and the log, questioning the assumptions about the tension in the ropes and the relationship between the movements of the blocks and the log. There is discussion about the implications of the rope's constant length on the accelerations of the masses.

Discussion Status

The discussion is ongoing, with participants providing insights and questioning each other's reasoning. Some participants have offered guidance on how to relate the lengths of the rope sections to the total length, while others are still trying to clarify their understanding of the relationships between the forces and movements involved.

Contextual Notes

Participants are grappling with the implications of the pulley system's configuration on the motion of the log and the blocks, particularly how the distances moved by the blocks relate to the acceleration of the log. There is an emphasis on writing equations to represent the physical relationships accurately.

  • #31
haruspex said:
No, you suggested the log would ascend 2m, which means each x would lose 2m. That would mean you start with L=y+2x, And end with a string length (y+1)+2(x-2)=y+2x-3=L-3. The string has mysteriously shrunk by 3m.
Try another way of changing x when y increases by 1m.
(y+1) + 2 (x-0.5) = y + 2x = L ?
 
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  • #32
Saints-94 said:
(y+1) + 2 (x-0.5) = y + 2x = L ?
Right. The log moves up half the distance that the weight moves down.
Based on that, if the weight descends at speed v, how fast will the log slide up the slope?
 
  • #33
0.5v?
 
  • #34
Saints-94 said:
0.5v?
Ok! Now for the one we've been working towards ... how will the accelerations compare?
 
  • #35
Will the acceleration be twice as much at the block compared to the log?
 
  • #36
Saints-94 said:
Will the acceleration be twice as much at the block compared to the log?
Yes.
But now I should confess something. The question posed is whether the log will move. To answer that, you do not need to worry about how fast it will move. You can suppose that it does not move, so there are no accelerations, and see whether the balance of forces is consistent with that.
However, most multiple pulley questions do involve different accelerations, and I felt it was important you found out how to deal with these.
 

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