- #1
Troubleshooting Tension: A Closer Look at Rotational Motion Calculations
- Thread starter freshbox
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Homework Help Overview
The discussion revolves around a problem related to rotational motion and tension in a system involving a compound pulley and attached masses. Participants are examining the relationship between angular acceleration, radius, and the forces acting on the system.
Discussion Character
- Conceptual clarification, Assumption checking, Problem interpretation
Approaches and Questions Raised
- Participants are questioning why the radius used in calculations should be the axle radius instead of the wheel radius, despite the problem stating it concerns the wheel's angular acceleration. There are discussions about the relationship between linear and angular acceleration and the significance of the attachment point of the rope.
Discussion Status
Some participants have provided guidance on using the correct radius for calculations based on where the rope attaches. There is an ongoing exploration of the implications of using different radii and how they affect the calculations. The conversation is productive, with participants clarifying concepts and addressing misunderstandings.
Contextual Notes
Participants are navigating through the constraints of the problem, including the need to relate linear and angular quantities and the definitions of forces acting on the system. There is a mention of multiple unknowns in the equations, which adds complexity to the discussion.
- #2
freshbox
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And if my answer is right... I want to ask the question states that "Angular acceleration compound pulley B is 5rad/s^2"
From this statement, why my radius is not the wheel radius (0.1) but I have to use the axle radius?
The whole wheel B is pulling mass A. shouldn't I use the wheel radius instead of the axle to find the acceleration?
More support to my statement: Wheel B And Parcel = Linear variables same. So all the more I should use Wheel radius to find acceleration.
From this statement, why my radius is not the wheel radius (0.1) but I have to use the axle radius?
The whole wheel B is pulling mass A. shouldn't I use the wheel radius instead of the axle to find the acceleration?
More support to my statement: Wheel B And Parcel = Linear variables same. So all the more I should use Wheel radius to find acceleration.
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- #3
Doc Al
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Yes, you should use the radius 0.1 because that's where the rope pulling A attaches.
- #4
freshbox
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Yea you are right, I sub in the values and got the exact answer.
Can I say for such questions to find acceleration, always use the radius that the rope is attaching to?
Can I say for such questions to find acceleration, always use the radius that the rope is attaching to?
- #5
Doc Al
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When you want the acceleration of the rope (which is the acceleration of the attached mass) then you want to use the radius where the rope attaches.freshbox said:
- #6
- #7
Doc Al
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Not sure what you mean. The angular acceleration is the same at any radius. (Don't confuse angular with linear acceleration.)freshbox said:
There are two forces of interest acting on the wheel. The torque produced by each force depends on where it is applied--that's the radius you'd use to calculate the torque.
- #8
- #9
Doc Al
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Again, do not confuse angular acceleration of the assembly, which is the same for wheel and axle, with the linear (or tangential) acceleration of some part of the wheel, which depends on the radius at that point.freshbox said:
In Equation 3, you are relating the linear acceleration a from Equation 2 to the angular acceleration. The linear acceleration is the acceleration of the rope and hanging mass. Where is the rope attached?
- #10
freshbox
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rope is attached to the axle.
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- #11
Doc Al
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Right. Thus to relate the linear acceleration of the rope (and thus the hanging mass) to the angular acceleration, you'll use the radius of the axle.freshbox said:
- #12
freshbox
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Does the wheel turn anticlockwise(because force 50N is pushing) and axle turning clockwise because Box A is pulling it down. Both turning different direction or the Wheel+Axle is turning together?
- #13
Doc Al
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The wheel + axle is a single connected assembly. It turns as one unit. (Thus wheel and axle have the same angular acceleration.)freshbox said:
- #14
freshbox
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Ok i understand it already, thanks a lot. Doc Al I have 1 last question, can you help me take a look.
I managed to find all the answers except for part E.
This is part of the working. My equation for FBD of Box C is as follow:
Summation Fy=ma
Tc-Wc=Mca
I have values for Tc, a, after subbing it in I have.
147.945-Wc=Mc(0.13)
I left 2 unknown which I am unable to continue.
I have look through the working from the FBD of Wheel and Box A but I cannot try to form an equation to find either Mc or Wc, can you guide me please. Thanks.
I managed to find all the answers except for part E.
This is part of the working. My equation for FBD of Box C is as follow:
Summation Fy=ma
Tc-Wc=Mca
I have values for Tc, a, after subbing it in I have.
147.945-Wc=Mc(0.13)
I left 2 unknown which I am unable to continue.
I have look through the working from the FBD of Wheel and Box A but I cannot try to form an equation to find either Mc or Wc, can you guide me please. Thanks.
Attachments
- #15
Doc Al
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You really only have one unknown. How are weight and mass related?freshbox said:
- #16
freshbox
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Weight = mass x 9.81
mass = Weight / 9.81
mass = Weight / 9.81
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- #17
Doc Al
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Right! Weight = mass X g.freshbox said:
So now you can solve for the mass of C.
- #18
freshbox
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Ahh... I got it already, thanks for the guidance and your time 