# Thread: Relative accelleration Problem

1. ## Relative accelleration Problem

Iam having some difficulty with this one iff some one could help.
What is the accelleration of point D (the centre)

2. Could you please give the problem statement in full?

3. There is a disk,it is ONE piece.It has a large diam and small diam.
The small dia rolls on a desk to the right.The large dia section does not touch the desk,but has a tangential acceleration as shown.
That is all that is known .
Find the accelleration of centre of the disk.

4. I think the thing to do is to find out the angular acceleration $\alpha$. Once you do that, you employ the (assumed) condition that the inner wheel rolls without slipping in order to translate the angular acceleration to linear acceleration. I do not think you have correctly computed the angular acceleration, although you have the correct general equation there:

$a_{\text{tan}}=r\,\alpha.$

Try computing that again. What do you get?

5. Thanks for that ,appreciated,I worked it out
ans is 15m/s^2 to the left

5m/s^2=r alpha
where r =(2-1.5) /2 (because where disk touches desk accell is 0 in the x directions) ie 5m/s^2 wrt desk.
alpha=20
accell of ctr = 20*1.5/2

6. Hmm. Not sure I agree. To start out, you'd have

5.0 m/s^2 = (1 m)(alpha), which implies alpha = 5.0 1/s^2. Then how would you continue?

7. oops,fixed up now,thanks

8. r =(2-1.5) /2
That is incorrect. You need to measure the radius from the center of both concentric circles to the outermost edge. Use the 1m I used.

9. Ok,I'll look into it thansk.