# Homework Help: Angular Velocities of rigid bodies at plane motionHelp me

1. Jun 19, 2011

Angular Velocities of rigid bodies at plane motion..Help me plz

Please Help for solve this problem.I realy need it.It looks like is but not for me ...
For the given positions
OA=0,3m ;
AB=0,6m ;
BC=0,3m ;
O1B=0,5m ;
ωOA=2 s-1 of the part OA from the mechanism , shown in the drawing.

DETERMINE :
1-) The linear veocities of points A , B and C
2-) The angular velocites of every part of the given mechanism

Note= If a disk is given , the motion is realized without sliding.

Here is the link for figure.
http://www.yukleresim.com/viewer.php?file=43049722008396930993.jpg" [Broken]

Last edited by a moderator: May 5, 2017
2. Jun 19, 2011

### Femme_physics

Re: Angular Velocities of rigid bodies at plane motion..Help me plz

You mean:

I think something got screwed in your text there.

----
Well, anyway, when you're given the angular velocity of a rotating object, and asked to find the tangential velocity of the vector at its edge, you just use the formula

V = ωR

V is what you're looking for, tangential velocity
ω is the angular velocity, in your case 2
R is the distance to the point/axis of rotation, in this case point O.

Can you get Va from that?

3. Jun 19, 2011

Re: Angular Velocities of rigid bodies at plane motion..Help me plz

Va = 0,6m/s ...but i am not sure others..Please help me for others..Because Va is easy..But others are hard for me because i am high school :(

4. Jun 19, 2011

### Femme_physics

Last edited by a moderator: May 5, 2017
5. Jun 19, 2011

Re: Angular Velocities of rigid bodies at plane motion..Help me plz

Thanks for Help ..Here is the my answers..But how can i find Vc...and angular velocities..

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6. Jun 19, 2011

### Femme_physics

Re: Angular Velocities of rigid bodies at plane motion..Help me plz

But your angle alpha is correct. I'm having a memory lapse with respect to beta-- I really need to see the exercise again.

If both angles are indeed 30 degrees than they are indeed equal (Va = Vb)...as far as Vc, well I'd like to see the diagram again.

7. Jun 19, 2011

Re: Angular Velocities of rigid bodies at plane motion..Help me plz

aha i am sory about this...Here you are....yes alpha and Beta i think are equal...and then Vc is equal too ...Now i need one more help for angulae velocities ....thanks again :)

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8. Jun 19, 2011

### Femme_physics

Re: Angular Velocities of rigid bodies at plane motion..Help me plz

Actually you need the beta of the third drawing. Oops. My bad, I defined beta differently in the last image. That's the beta you need. You'll find out that's 60.

So it's really should be

Vacos(30) = Vbcos(60)

Which means they aren't equal.

As far as Vc, it's definitely not equal to the rest of them, but we'll get to that later. First you need to find P, the instanteneous axis of rotation,

I'd advise you to look at this image as an example problem to see how they locate P:

[PLAIN]http://img3.imageshack.us/img3/8868/solman222.jpg [Broken]

Its location should be quite obvious, it's where the two tails of Va and Vb meet. You can use this formula:

To find omega of that particular shaft.

Notice that the radius is the distance from Va to the instantaneous axis of rotation

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9. Jun 19, 2011

Re: Angular Velocities of rigid bodies at plane motion..Help me plz

Thanks for the hint :)...Here is the my answer can you please check it ..First picture is for the point P..I draw The all necessary points and shafts. Second picture is for the solving way...I am realy glad to meet you :) ( sory for my language its not my main )

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10. Jun 19, 2011

### Femme_physics

Re: Angular Velocities of rigid bodies at plane motion..Help me plz

Happy to help :)

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Are you telling me that the distance from Vc to P and the distance from Vb to P are equal?

Look at the trigonometry, see if it makes sense.

To make think simpler, here is how you find the angular velocity of AB (I'm not familiar with the formula you used)

http://img691.imageshack.us/img691/2336/thisformula.jpg [Broken]

You know Va, you know its angle to AB, you know Vb, you know its angle to AB, and you know the length. You can solve for omega

Last edited by a moderator: May 5, 2017