Question

Please see pic
A sphere of mass Msphere and a yoyo of mass Myoyo are suspended from a from a pulley with mass Mpulley. The pulley can rotate with negligive friction about its fixed pivot. αyoyo and αpulley are angular accelerations.

The sphere and the yoyo are released from rest and reach the ground at the same time. Answer: greater than less than equal to
The yoyo's linear acceleration is ... that of the sphere.
Taking counter-clockwise as (+), and clockwise as (-) , αyoyo ... zero.
Msphere is ... Myoyo.
Tension Tz is ... tension Tx.

Answer 1

0_o what an atrocious problem....

Answer 2

Yes, tell me about it. This is extra credit for the last exam, and i did very badly and need every point i can get. :( Also, perhaps I can really grasp these concepts.

Answer 3

hmmmmmm...... there isn't even one correct answer; some of it's dependent on how you answer the third question! sheesh :P

Answer 4

Any insight you have as to knowing any of the answers, can maybe give me some missing pieces. 2 heads.....

Answer 5

Well, the third one has to be clockwise, because the left side of the yoyo is being pulled up and the right ride is falling down... does that make sense?

Answer 6

err, second one

Answer 7

it makes some sense, :) but is it falling down or rolling down? I'd like to know bc ill need it for another problem-the equations are different.

Answer 8

It's definitely rolling down, along the little radius (w/o slipping I think, otherwise it's no fun)

Answer 9

LOL! okay, this is a good start.
Next, does it roll faster than a sphere would fall?

Answer 10

Well, if they hit the ground at the same time, I think it would have to roll faster, because if it were were equal then the yoyo would remain stationary, right? *I have not proven that mathematically so am not 100% sure....

Answer 11

what do you mean remain stationary? Not fall to the ground?

Answer 12

stationary in space - if the sphere fell just as quickly as the yo yo rolled, then the center of the yo yo would stay in the same place in space while the sphere dropped to the ground. I think....

Answer 13

because it would be unwinding the cord as quickly as the sphere pulled it out.

Answer 14

omg, you have something here. Another problem had one of the yoyos staying in the same place as the sphere fell.
So what is happening here? Its sad that this is not clear to me.

Answer 15

Here is the case I discussed as attached.

Answer 16

There is nothing whatsoever intuitive about yoyo physics :P

Answer 17

So that one, the total force on the yo yo has to be zero, since it's not linearly accelerating I think....

Answer 18

but isnt the sphere linearly accelerating? or at least its Center of mass?

Answer 19

Also, is a yoyo a sphere?
or cylinder/

Answer 20

The sphere is definitely linearly accelerating - and it's not that there aren't any forces acting on the yoyo, it's that they cancel out.

The yo yo would be a cylinder of sorts...