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Some More Problems



Howdy,

Here are a couple of my favorite problems relating to rotational motion. I
use them as sample applications in my Engineering Physics class.

1) Imagine a tricycle wheel (direct drive through the pedals) with the
pedals vertical which is free to roll without slipping. Apply a constant
force to the BOTTOM pedal (to the right in this example). The force is NOT
large enough to cause the wheel to slip over then surface. What is the
direction of acceleration of the wheel (and why!)?

I usually start off the first problem by applying the force to the top
pedal and asking the students the direction of the acceleration: an obvious
answer. When I switch to the bottom pedal I get lots of controversy.
Sometimes I take a vote and the classes first instincts are almost always
wrong!

The second problem can be done in a straight forward way in about 15-20
minutes but can be done very quickly if you really understand the
underlying Physics. Hint: be careful about the coordinate system you
choose for the problem.

2)Consider a bowling ball to be an uniform solid sphere (i.e., we neglect
the holes drilled into the ball). A certain bowling ball is released in
such a way the its CM is moving with a speed 'v' along the bowling alley
without rolling (i.e., slipping without rolling). Because of the kinetic
friction force between the ball and the alley the ball starts to roll as it
slides along the surface. What is the speed of the CM of the ball at the
moment it is rolling without slipping?

Hope you enjoy them,

Herb Schulz
(herbs@interaccess.com)