# rolling and sliding objects

*From*: "katy" <mcld@xxxxxxxxxxxxxxx>*Date*: 1 May 2006 15:48:40 -0700

Hi all!

I'm having some problems with rolling and sliding objects..

For example,

I have an homogeneous sphere with radius of 10 cm.

P=5N

It is moving in an horizontal and flat superficie until point A with

a constant velocity of 5m/s,

then from point A until point B the superficie is rough and the

coeficient of kinetic friction is 0.1.

In B the sphere start rolling without sliding.

The following diagram tries to explain the sphere path:

____A /\/\/\/\/\/\ B

The question is:

Find the kinetic energy in B

the mass of the sphere is iqual to 5/9.8 ~= 0.51

In B the sphere is not sliding and is only rolling, so that

Kinetic energy in B = Kinetic rotational energy in B = 1/2 I w^2

where I is the momentum of inertia that is equal to 2/5 M R^2

Ekb=1/2 *2/5 *M*R^2 * w^2

Ekb=1/5*0.51*0.1^2*w^2

Ekb=0.001 w^2

So, my problem is how can i found w?

i thouth in the formula v=w *r

But, in B the sphere is not sliding so, v = 0

Can somebody help me please?

Thanks,

Catarina Dias

.

**Follow-Ups**:**Re: rolling and sliding objects***From:*Fredrik Bulow

**Re: rolling and sliding objects***From:*CWatters

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