Re: [Phys-l] October Physics Challenge

[brian whatcott <betwys1@sbcglobal.net>]

On 11/6/2010 6:55 PM, Carl Mungan wrote:
> > 3) The setup is manipulated to start the large block slipping first
> > by holding the small mass and ribbon in place at a high inclination:
> > The ribbon and small mass descend uninhibited at m.g. sin(theta)
> > the ribbon tension is zero, the large block descends at M.g.sin(theta)
> >
> > This result is unsurprizing, and so it is not the case that you find interesting, which must occur when mu_k/mu_s = m/M, at the largest mu_k for consideration.
> > But I will pause at this point, in case I am missing the crux.
> >
> > Brian W
> No, it probably does correspond to my case, if you turn mu_k back on.
>
> The real question is: Is it fair to suppose that such a case can occur? Someone else has suggested that we think of each block initially held in position by an upward force, each of which is simultaneously reached. The ribbon has to stretch a bit before the blocks can slip, so that is what the idea of the small block slides "first" means. What do you think?
Ah you are dealing with the consequences of imputing a particular method 
of holding the small mass and ribbon. You visualize a stretchable ribbon 
(shame on you, this is meant to be a physicist';s ribbon!   :-)   and 
the upward force is I suppose an upslope foce to balance the down slope 
gravity vector.
For some reason, I imagined a clamp appling a normal force to the small 
mass, so the large block can stretch the ribbon as desired while the 
ramps grow more
high-pitched, so to speak.... would that resolve the issue?

Brian W