Rotational Mechanics: Comparing Cylinder P & Q

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Discussion Overview

The discussion revolves around the comparison of two solid cylinders, P and Q, with the same mass and radius, rolling down an inclined plane. Participants explore concepts related to moment of inertia, the instantaneous axis of rotation, and translational kinetic energy, focusing on theoretical aspects of rotational mechanics.

Discussion Character

  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant questions which cylinder has a greater moment of inertia, suggesting that cylinder P, with mass concentrated near its surface, could be treated as a hollow cylinder with a moment of inertia of MR², while cylinder Q, with mass near the axis, could be treated as a solid cylinder with a moment of inertia of MR²/2.
  • Another participant agrees with the assessment of moment of inertia, stating that P has a greater moment of inertia than Q, but notes that assuming P as a hollow cylinder is an extreme case and questions the generality of the original problem.
  • Questions are raised about the instantaneous axis of rotation and whether both cylinders reach the ground with the same translational kinetic energy, but these points have not yet been addressed in detail.

Areas of Agreement / Disagreement

There is some agreement on the moment of inertia calculations, but the discussion remains unresolved regarding the instantaneous axis of rotation and the translational kinetic energy of both cylinders.

Contextual Notes

The discussion relies on assumptions about the distribution of mass in the cylinders and the definitions of moment of inertia. The implications of these assumptions on the broader context of the problem are not fully explored.

joker94
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Two solid cylinders p and Q of same mass and same radius start rolling down a fixed inclinded plane from the same height at the asme time.cylinder P has most of its mass concentrated near its surface while Q HAS MOST of its mass near the axis...
THEN
1)WHICH HAS MORE MOMENT OF INERTIA AND WHY?
2)WHAT IS THE INSTANTEOUS AXIS OF ROTATION??
3)DOES BOTH CYLINDERS REACH THE GROUND WITH SAME TRANSLATIONAL KINECTIC ENERGY?
 
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welcome to pf!

hi joker94! welcome to pf! :wink:

tell us what you think, and then we'll comment! :smile:
 
hi...can we consider P as a hollow cylinder then moment of inertia about the axis(which is passing through its centre) would be MR^2...AND THEN WE CAN CONSIDER Q AS A SOLID CYLINDER HAVING MOMENT OF INERTIA MR^2/2 (^2 MEANS SQUARE AND / DIVIDE)...SO IT MEANS MOMENT OF INERTIA OF P IS MORE THAN MOMENT OF INERTIA OF Q.!
AM I CORRECT?
 
joker94 said:
hi...can we consider P as a hollow cylinder then moment of inertia about the axis(which is passing through its centre) would be MR^2...AND THEN WE CAN CONSIDER Q AS A SOLID CYLINDER HAVING MOMENT OF INERTIA MR^2/2 (^2 MEANS SQUARE AND / DIVIDE)...SO IT MEANS MOMENT OF INERTIA OF P IS MORE THAN MOMENT OF INERTIA OF Q.!
AM I CORRECT?

Right answer, though of course it would be better not to have to assume the extreme case when the original question was posed more generally.
How about your questions 2 and 3?
 

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