Need help, to help, a friend with their HW (High School)

[Owen Ploe]

Homework Statement

I am currently helping a friend with their physics HW as they are unable to do it. They are taking AP and I am not. So they have covered about 4 times as much material as I have.

Relevant Equations

ω = (ωo + ωf) / 2, L = I ω and others

This is the problem set. I am stuck from this point... If anyone could give me a hand I would really appreciate it. I know this is probably really simple, but I don't know any of this and have been trying my best with youtube, and other peoples posts.
PS this is for high school

 

[haruspex]

Homework Statement: I am currently helping a friend with their physics HW as they are unable to do it. They are taking AP and I am not. So they have covered about 4 times as much material as I have.
Relevant Equations: ω = (ωo + ωf) / 2, L = I ω and others

View attachment 344021
This is the problem set. I am stuck from this point... If anyone could give me a hand I would really appreciate it. I know this is probably really simple, but I don't know any of this and have been trying my best with youtube, and other peoples posts.
PS this is for high school

Using one of the relevant equations you quote, you should be able to fill in the last column of the first row easily. That gives you one way to calculate last column, last row.
Let the resulting rotation rate of the system be ##\omega## ( middle column, last row). That gives you another equation for last column, last row.

 

[Owen Ploe]

Using one of the relevant equations you quote, you should be able to fill in the last column of the first row easily. That gives you one way to calculate last column, last row.
Let the resulting rotation rate of the system be ##\omega## ( middle column, last row). That gives you another equation for last column, last row.

I got the first column. What I don't know is how to get the angular velocity of the student running, and then how I combined those two together.
Im sure this is really simple and kinda a stupid question. But thank you for helping me

 

[haruspex]

What I don't know is how to get the angular velocity of the student running

Then who wrote "2.79” under rad/s?

and then how I combined those two together

As I wrote, refer to the relevant equations in post #1. There are only two, and the other one is not relevant to this question.
Two more relevant equations:
Moment of Inertia of composite object about a given axis equals sum of MoIs of the individual components about that axis.
Angular Momentum of composite object about a given axis equals sum of AMs of the individual components about that axis.

 

[Owen Ploe]

Then who wrote "2.79” under rad/s?

My friend wrote the "2.79" and it was incorrect, the answers highlighted green are correct.

Angular Momentum of composite object about a given axis equals sum of AMs of the individual components about that axis.

So basically, the angular momentum of the combined objects, is just AM of object one plus AM of object 2.
How do you find the AV of the student running? I know you can find it by AM/Rotational Inertia = AV
But I don't have the Rotational Inertia given to me.

 

[haruspex]

My friend wrote the "2.79" and it was incorrect

That's because linear velocity = radius x angular velocity. Your friend did angular velocity = radius x linear velocity. You can see that must be wrong by filling in the dimensions. Radius is a length, velocity is length/time, so radius x linear velocity would be length x length / time instead of 1/time.

the angular momentum of the combined objects, is just AM of object one plus AM of object 2.

Yes.

 

[Owen Ploe]

That's because linear velocity = radius x angular velocity. Your friend did angular velocity = radius x linear velocity. You can see that must be wrong by filling in the dimensions. Radius is a length, velocity is length/time, so radius x linear velocity would be length x length / time instead of 1/time.

Yes.

Thank you for all your help! I got all parts of the problem done. It was supper help full. Sorry some of my stuff was probably stupid.