I just received a flyer in my mailbox advertising a "Homework Service."
The URL for this is http://hw.ph.utexas.edu/hw.html, so I'm guessing it's
from U Texas at Austin. They give two examples of problems and their
solutions. One is the standard "Atwood Machine" in which one block is
sliding across a table while the other is suspended from a string passing
over a pulley. The masses are 4.13 kg and 5.48 kg and when the hanging
mass has fallen a distance of 0.426 m, its downward speed is 1.3 m/s. Got
all that? They ask what is the coefficient of friction between the sliding
block and the table. Now guess what they give as the answer?
After showing that the acceleration is a = 1.98357 m/s^2, the coefficient
of friction is determined to be
mu = 0.398702
And then they get the tension in the cord:
T = 32.2819 N
I'm guessing this has all come from a physics department, or at least from
someone who is supposedly knowledgeable about physics. If this kind of
sloppiness is routine, I would sure think twice about such a service. I
guess we don't do much with significant figures anymore, and this is what
can happen.
------------------------------------------------------------------------------
Van E. Neie ven@physics.purdue.edu
Dept of Physics PH: (765) 494-5511
Purdue University FAX: (765) 494-0706
1396 PHYS Bldg
W. Lafayette, IN 47907-1396
"There ain't no rules around here! We're trying to accomplish something!"
--Thomas Alva Edison