Re: [Phys-l] A Mechanics Question

[Brian Whatcott <betwys1@sbcglobal.net>]

At 09:13 AM 6/1/2008, Michael E., you wrote:
> Actually, since the roof is shingled, as usual, once the frisbee hits the
> roof and begins to slide upward, it hits the edge of a shingle and it flips
> over.  Now it slides down the roof with its curved side facing downward, and
> its friction is quite low, and as it picks up downward speed it almost lifts
> off the roof and skims primarily with air friction.  When it sails off the
> roof, Billy catches it.  We are unable to answer the question of how far it
> landed from Billy's feet because we are not told how tall Billy is.
> However, if he catches it at roughly the same height as he threw it, then it
> is one meter from his feet.
>
> On the other hand, if the frisbee did not flip, then it becomes stuck on the
> roof because the sharp edges of the bottom edge of the frisbee stick on the
> granules of the shingles.  I know this from childhood experience, having had
> to get the ladder out to retrieve any frisbee that did not flip on its top
> when it hit the roof.  I have a lot of experience climbing the ladder.
>
>
> Michael D. Edmiston, Ph.D.
> Professor of Chemistry and Physics
> Bluffton University
> 1 University Drive
> Bluffton, OH 45817
> 419.358.3270
> edmiston@bluffton.edu

Michael is pointing to a certain lack of plausibility here, which
might be described as "mu is variable and at times reaches
high integer values(!)". However, the instructor has specified,
"..the frisbee [slides] up the roof before continuing past
the house" so we can easily suppose a corrugated aluminum roof
or something of that kind.

I can add that the instructor adds finally,
"Assume the frisbee hits the roof with the initial velocity."

[This was apparently a junior college level assignment.]


Brian Whatcott    Altus OK    Eureka!