Friction on an Inclined Plane
Two blocks of masses M1
and M2 are joined by a string over a pulley attached to an
inclined plane. To simplify the problem, we will set the mass M2
to zero and only be concerned with the motion of the mass M1
as it slides down the ramp against friction. Forget all about M2
– pretend it isn’t there!
Questions:
-
Make a prediction:
Imagine you have three blocks, all exactly
alike except that their masses are 5, 10, and 20 kg. The coefficient of
friction between each block and the ramp is the same. The angle of the ramp
with the horizontal is 30°. If each
block was released from rest near the top of the ramp, predict which one you
think would have the largest acceleration. Explain briefly why you chose that
block. (Note that your mark is based on your explanation, not whether it is
correct!)
-
Now load the physlet:
http://lectureonline.cl.msu.edu/~mmp/kap4/cd095a.htm
Be sure to wait until the applet has finished loading before you begin.
Set up the physlet so that
the ramp angle is 30°, the
coefficient of kinetic friction m
= 0.24, and mass M1 = 5 kg. (Don’t forget to set M2
= 0!) Run the physlet and record the acceleration of the 5 kg block. Then
repeat for M1 = 10 kg and then 20 kg, recording the
acceleration each time. How does your prediction compare to what you observe
for the three blocks?
-
Use a free-body diagram and
Newton’s second law to derive an expression (i.e. no number values) for
the acceleration of the block in terms of M, g,
m and the angle
q. Do you notice anything in the
expression you derived that accounts for the observed acceleration of the
three blocks?
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