Assignment 3
Due: 11:59pm on Sunday, March 24, 2013
Note: You will receive no credit for late submissions.
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Problem 1
Learning Goal:
To practice Problem-Solving Strategy 6.1 Circular dynamics problems
A 1500-
car drives at 30
around a flat circular track 300
in diameter. What are the magnitude and
direction of the net force on the car?
PROBLEM-SOLVING STRATEGY
Circular dynamics problems
PREPARE
Begin your visual overview with a pictorial representation in which you sketch the motion, define
symbols, define axes, and identify what the problem is trying to find. There are two common situations:
If the motion is in a horizontal plane, like a tabletop, draw the free-body diagram with the circle
viewed edge-on, the
-axis pointing toward the center of the circle, and the y-axis
perpendicular to the plane of the circle.
If the motion is in a vertical plane, like a Ferris wheel, draw the free-body diagram with the
circle viewed face-on, the
-axis pointing toward the center of the circle, and the
-axis
tangent to the circle.
SOLVE
Newton’s second law for uniform circular motion,
, is a
vector equation. Some forces act in the plane of the circle, some act perpendicular to the circle, and some
may have components in both directions. In the coordinate system described above, with the
-axis
pointing toward the center of the circle, Newton’s second law is
and
.
That is, the net force toward the center of the circle has magnitude
, while the net force
perpendicular to the circle is zero. The components of the forces are found directly from the free-body
diagram. Depending on the problem, do one of the following:
Use the net force to determine the speed
, then use circular kinematics to find frequencies or
angular velocities.
Use circular kinematics to determine the speed
, then solve for unknown forces.
ASSESS
Make sure your net force points toward the center of the circle. Check that your result has the
correct units, is reasonable, and answers the question.
Prepare
Physics with Lab
Assignment 3
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Assignment 3
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2013-03-23 5:14 PM