A . ile't
Student
Class
Date
Circular Motion 2
1.
There is a clever kitchen gadget for drying lettuce leaves after
you ~ash them. It consists of a cylindrical container mounted so
that it can be rotated about its axis by turning a hand crank.
The outer wall of the cylinder is perforated with small holes.
You put the wet leaves in the container and turn the crank to
spin off the water. The radius of the container is 12 cm. When
the cylinder is rotating at 2.0 revolutions per second, what is
the magnitude of the centripetal acceleration at the outer wall?
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2.
.
Friction provides the centripetal force necessary for a car to
travel around a flat circular-race track. What is the maximum
speed at which a car can safely travel around a circular track of
radius 80.0 m if the coefficient of friction between the tire and
road is 0.30?
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3.
Friction provides the centripetal force that allows a 1,600 kg
car to round a curve of radius 80. meters at a speed of 20.
meters per second.
a) Calculate the minimum coefficient of friction needed between
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b) If the mass of the curve were increased, how would that affect
the maximum speed at which it could round the curve?
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At amusement parks, there is a popular ride where the floor of a
rotating cylindrical room falls away, leaving the backs of the
riders Uplastered" against the walls. Su.ppose the radius o.fthe
room is 3.30 m and the speed of the wal~ is 10.0 m/s when the
floor falls away.
a) What is the source of the centripetal
.riders?
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b) How much centripetal force/~cts
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on a 55.0 kg rider?
c) What is the mInImum coefficient of static friction that must
exist between a rider's back and the wall, if the rider is to
remain in place when the floor drops away?
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5.
Two students, Julia and Tom, decided to perform an experiment to
verify Newtown's Second Law as applied to uniform circular
2
motion: that is ~ =~.
In the lab, they collected
the following
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materials: IS-centimeter long glass tube, fire-polished at each
end and covered with rubber tubing, a piece of nylon' l~ne
'approximately one meter long, several two-holed rubber stoppers,
a paper clip, masking tape, 36 identical iron washers, a
stopwatch, and a triple-beam balance. An apparatus was assembled,
with the intention of using it as shown below.
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a) As the first objective Tom wrote: "To determine the
relationship between the velocity of an object moving in a
circular path and t~e magnitude of the centripetal force acting
on the object." Julia objected stating they could collect data
that enable them to determine the average speed of the rubber
stopper in a circular path, but not its velocity. Identify which
student was correct and explain why.
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b) Describe how the number of washers suspended at one end of the
nylon cord could be converted into a measurement of the magnitude
of the centripetal force acting on the stopper.
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c) To avoid having to use either the term velocity or speed, Tom
changed their first objective to: ceTo determine the relationship
between the period of revolution of an object moving in a
circular path and the magnitude of the centripetal force acting
on it." Using formulas found on the Reference TabLes for PhysicaL
Setting/Physics, derive an expression for centripetal force in
terms of r the radius of the curvature of the path, m the
object's mass, and T the period of the revolution.
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d) The pair decided to time the motion of the stopper for thirty
revolutions instead of making three separate trials of one
revolution each and calculating tan average to determine its
period. Provide a rationale for this decision.
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e) After securing all essential materials" the pair proceeded
with the collection of data. Julia practiced swinging the stopper
overhead in a horizontal path" while keeping the radius of the
path fixed. Once the technique was mastered the number of washers
was varied for each trial in increments of 4 washers. Tom timed
each event. Identify four essential pieces of information that
the students should have recorded in their data table.
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f) After the data was collected the students decided to graph
their results. Sketch the general shape of the graph that should
result for period of revolution versus magnitude of centripetal
force. Label the axis with the dependent and independent
variables.
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period that they had not sufficient time to verify Fc=---.
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