How Does Impact Affect Angular Momentum and Velocity in a Rotating Disk System?

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Homework Help Overview

The problem involves a rotating disk system where a lump of clay impacts the disk, affecting its angular momentum and velocity. The disk has a specified mass and radius, and the clay's mass and speed before impact are given. The discussion centers on calculating the angular momentum of the system before and after the impact, as well as determining the angular velocity of the disk post-impact.

Discussion Character

  • Exploratory, Mathematical reasoning, Assumption checking

Approaches and Questions Raised

  • Participants discuss the calculation of angular momentum, considering the contributions from both the disk and the clay. There are questions about the moment of inertia of the disk and how to incorporate it into the angular momentum calculations. Some participants express uncertainty about the initial conditions and the necessary equations.

Discussion Status

The discussion is ongoing, with participants attempting to clarify the calculations related to angular momentum. Some guidance has been offered regarding the moment of inertia, but there is still uncertainty about the overall approach and the inclusion of units in the calculations.

Contextual Notes

Participants note a lack of clarity regarding the initial angular momentum and the necessary equations to solve the problem. There is an emphasis on ensuring that all components are considered in the calculations.

luckyg14
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Homework Statement


A rotating uniform-density disk of radius 0.6 m is mounted in the vertical plane. The axle is held up by supports that are not shown, and the disk is free to rotate on the nearly frictionless axle. The disk has mass 5.8 kg. A lump of clay with mass 0.5 kg falls and sticks to the outer edge of the wheel at location A, < -0.36, 0.480, 0 > m. (Let the origin of the coordinate system be the center of the disk.) Just before the impact the clay has a speed 8 m/s, and the disk is rotating clockwise with angular speed 0.83 radians/s.



1) Just before the impact, what is the angular momentum of the combined system of wheel plus clay about the center C? (As usual, x is to the right, y is up, and z is out of the screen, toward you.)
LC,i = ?kg · m2/s

2) Just after the impact, what is the angular momentum of the combined system of wheel plus clay about the center C?
LC,f = ?kg · m2/s

3) Just after the impact, what is the angular velocity of the wheel?
omega vecf = ?radians/s


Homework Equations


I have no clue


The Attempt at a Solution


I don't know how to do it
 
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luckyg14 said:
1) Just before the impact, what is the angular momentum of the combined system of wheel plus clay about the center C? (As usual, x is to the right, y is up, and z is out of the screen, toward you.)
LC,i = ?kg · m2/s
Angular momentum has units like kg.m/s.
The angular momentum of the combined system about C is the sum of the individual angular momenta about C.
What is the moment of inertia of the disc about its centre?
 
I=.5*m*r^2
=.5*5.8*.6^2
=1.044
 
luckyg14 said:
I=.5*m*r^2
=.5*5.8*.6^2
=1.044
Right, but don't forget to include units.
You know the initial rate of rotation of the disc, so what is its angular momentum about its centre?
 

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