How Does an Impulse Affect the Angular Momentum of a Spinning Wheel in Space?

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Homework Help Overview

The discussion revolves around a problem involving a spinning wheel in outer space, specifically focusing on how an applied impulse affects its angular momentum. The wheel is described as a ring with a defined radius and mass, spinning at a specified angular velocity when an impulse is applied.

Discussion Character

  • Exploratory, Assumption checking, Conceptual clarification

Approaches and Questions Raised

  • Participants explore the relationship between angular impulse and angular momentum, questioning how to convert impulse units into angular momentum components. There is discussion on calculating torque impulse and the relevance of certain equations to the problem.

Discussion Status

Participants are actively questioning the correctness of initial equations and discussing the necessary relationships between angular momentum, moment of inertia, and angular impulse. Some guidance has been offered regarding the need to express angular momentum in consistent units and the use of Pythagorean theorem for combining components.

Contextual Notes

There are indications of confusion regarding the definitions and relationships between impulse, angular impulse, and torque impulse. The problem setup includes specific constraints such as the shape and mass of the wheel, as well as the nature of the applied impulse.

24forChromium
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Homework Statement


A wheel spins in outer space, it is in the shape of a ring (negligible thickness) with a radius of 1 meter and a mass of 1 kilogram, it is spining at π Radian/sec around its central axis (z-axis) in a fashion that is like any other car wheel. Just then, an impulse of 10N*sec was applied on its left side with a direction pointing straight up (z). What are the components of the final angular momentum?

(There's a picture. Hopefully the picture works)

Homework Equations


Moment of inertia = mass * radius
angular acceleration = torque / angular inertia
torque = lever arm length * force

The Attempt at a Solution


First, the impulse causes an angular impulse on the ring, sadly I don't know how to convert N*sec to meter*kilogram*Radian/sec, if that's what angular impulse look like at all. Then, this angular impulse creates a new component of angular momentum in the y-axis, and at last, add the original angular momentum with the new angular momentum, use pythagorean theorem and trignometry to calculate the final angular momentum.

Ring in outerspace.jpg
 
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If the radius of the ring is 1 meter and the impulse of the force is 10 N*sec, what is the torque impulse?
 
Your first relevant equation is wrong, and the other two are not relevant to this question. You do need one relating angular momentum to moment of inertia.
You don't need to convert the N sec. What you do need to do is find the original angular momentum and the added angular momentum in the same units. What units seem appropriate?
Using Pythagoras to combine them is correct.
 
haruspex said:
Your first relevant equation is wrong, and the other two are not relevant to this question. You do need one relating angular momentum to moment of inertia.
You don't need to convert the N sec. What you do need to do is find the original angular momentum and the added angular momentum in the same units. What units seem appropriate?
Using Pythagoras to combine them is correct.
why is the first one wrong and what do you think it should be?
I am only given angular impulse, how can I translate that to angular momentum?
 
Chestermiller said:
If the radius of the ring is 1 meter and the impulse of the force is 10 N*sec, what is the torque impulse?
Sorry, what do you mean by "torque impulse"?
 
24forChromium said:
why is the first one wrong and what do you think it should be?
Moment of inertia has dimension mass * distance2. Your equation has it as just mass * distance.
24forChromium said:
I am only given angular impulse, how can I translate that to angular momentum?
No, you are given an impulse. You need to calculate the resulting angular impulse. Angular impulse is the same as change in angular momentum.
 
24forChromium said:
Sorry, what do you mean by "torque impulse"?
I mean angular impulse.
 

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