Calculating Final Angular Velocity of Turntable with Runner on a Horizontal Axis

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The discussion revolves around calculating the final angular velocity of a turntable when a runner slows to a stop relative to the Earth. The problem involves a 55 kg runner with a velocity of 3.1 m/s on a turntable rotating at 0.20 rad/s. Participants express confusion over the calculations, particularly regarding the definitions of variables and the clarity of the working shown. The initial and final angular momenta of the system are considered, with one participant arriving at a final angular velocity of -4.06 rad/s. The conversation emphasizes the importance of clear variable definitions and presentation in solving physics problems.
reminiscent
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Homework Statement


A 55 kg runner runs around the edge of a horizontal turntable mounted on a vertical, frictionless axis through its center. The runner's velocity relative to the Earth has magnitude of 3.1 m/s. The turntable is rotating in the opposite direction with an angular velocity of magnitude 0.20 rad/s relative to the earth. The radius of the turntable is 3.0 m, and its moment of inertia about the axis of rotation is 120 kg-m2. Find the final angular velocity of the turntable if the runner slows to a walk in such a way that she is at rest relative to the earth.

Homework Equations


ΔL = 0
L1 = L2

The Attempt at a Solution


This was ripped off from a problem in the book that asked for "the final angular velocity of the system if the runner comes to rest relative to the turntable," which I did just that, but I just noticed that this problem's last sentence is a different variation (final angular velocity of the turntable if the runner slows to a walk in such a way that she is at rest relative to the earth.")
Here is what I did - should I change anything at the end?
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Your working is not easy to read (posting images is for diagrams and printed/typed matter) and you do not define your variables, which makes it hard to follow.
I get a different answer.
 
haruspex said:
Your working is not easy to read (posting images is for diagrams and printed/typed matter) and you do not define your variables, which makes it hard to follow.
I get a different answer.
Well T stands for turntable and R stands for runner. L1 was the initial and L2 was the final. L1 consisted of the angular momentums of both the turntable and runner. I treated them as a system at the end having the same angular velocity.
 
Can anyone tell me what I did wrong?
 
haruspex said:
Your working is not easy to read (posting images is for diagrams and printed/typed matter) and you do not define your variables, which makes it hard to follow.
I get a different answer.
I got a new answer of -4.06 rad/s.
 
reminiscent said:
I got a new answer of -4.06 rad/s.
That's right.
 
The book claims the answer is that all the magnitudes are the same because "the gravitational force on the penguin is the same". I'm having trouble understanding this. I thought the buoyant force was equal to the weight of the fluid displaced. Weight depends on mass which depends on density. Therefore, due to the differing densities the buoyant force will be different in each case? Is this incorrect?

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