Torque and Forces in Spool Movement: Solving for Net Torque and Static Friction

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Homework Help Overview

The discussion revolves around analyzing forces and torques in the context of a spool's movement, specifically focusing on static friction and net torque calculations. Participants are exploring the relationships between various forces acting on the spool.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • Participants discuss the balance of forces in both x and y directions, questioning the setup of the equations for net torque. Some suggest examining the implications of specific values for radius and angle, while others recommend reconsidering the choice of axis for torque calculations.

Discussion Status

There are multiple interpretations being explored regarding the calculation of torque and the forces involved. Some participants have expressed confidence in their solutions, while others continue to question the assumptions and setup of the problem.

Contextual Notes

Participants note that the problem is presented as a multiple-choice question, which may influence their reasoning and approach to eliminating options based on physical intuition.

jaewonjung
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Homework Statement
Problem in picture
Relevant Equations
Fnet=ma
Forces in the x direction: static friction left=Tcostheta to the right
Forces in the y direction: W= Normal force + Tsintheta
Net torque: rTcostheta-RFs=0

Fs=Tcostheta,
rTcostheta-R(Tcostheta)=0
rTcostheta=RTcostheta
r=R

Please help
 

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This is a multiple choice question, so try to use intuition about rolling vs slipping to eliminate answers. Look at each variable in turn: for instance what if r=R? Will it roll? Then think about theta...what if it is zero...90deg...
 
jaewonjung said:
Net torque: rTcostheta-RFs=0
Looks like you are taking moments about the centre of the cylinder. Think again about the torque due to T. Maybe draw a nice big picture, carefully.
(There is a better choice of axis for this problem.)
 
I solved it! The torque of the Tension is just Tr, not Trcostheta. Thanks for the help!
 
jaewonjung said:
I solved it! The torque of the Tension is just Tr, not Trcostheta. Thanks for the help!
Good.
Note that if you take moments about the point of contact with the ground instead it becomes a matter of simple geometry.
 

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