Physics 1A Winter 2009: Quiz 5
Version A
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Closed book. No work needs to be shown for multiple-choice questions.
1. A wheel initially has an angular velocity of 18 rad/s but it is slowing at a rate of 2.0 rad/s2
until it comes to a stop. By the time it stops it will have turned through:
-> (a) 80 rad.
(b) 160 rad.
(c) 200 rad.
(d) 300 rad.
(e) 400 rad.
2. If a wheel is turning at 3.0 rad/s, the time it takes to complete one revolution is about:
(a) 0.3 s.
(b) 0.6 s.
(c) 1.0 s.
(d) 1.3 s.
-> (e) 2.0 s.
3. What centripetal acceleration does an 80 kg person experience when seated 12 m from the
center of a merry-go-round whose angular speed is 0.50 rad/s?
(a) 20 m/s2.
(b) 10 m/s2.
->(c) 5 m/s2.
(d) 30 m/s2.
(e) 0.1 m/s2.
4. A 0.30-kg rock is swung in a circular path and in a vertical plane on a 0.25-m-length string.
At the top of the path, the angular speed is 12.0 rad/s. What is the tension in the string at that
point?
->(a) 8 N.
(b) 16 N.
(c) 18 N.
(d) 80 N.
(e) 140 N.
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Physics 1A Winter 2009: Quiz 5
Version A
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5. An ice skater with a moment of inertia of 70.0 kg ! m2 is spinning at 4.1 rad/s. If the skater
pulls in her arms, her rotational inertia decreases to 50.0 kg ! m2 . What is the skater’s
resulting angular speed?
->(a) 5.7 rad/s.
(b) 2.9 rad/s.
(c) 4.9 rad/s.
(d) 2.1 rad/s.
(e) 8.5 rad/s.
6. Two wheels of different radii are stuck together on an axle through their centers. They are thus
free to rotate together around their common axis. Forces as indicated in the figure are applied at
the rim of each wheel. Which of the following statements is correct:
(a) the wheels are turning counterclockwise only if F > f.
(b) the wheels are turning clockwise if F = f.
->(c ) the wheels are turning counter clockwise if F = f
(d) the wheels are turning clockwise if F > f.
7. A uniform ladder 10.0 m long and weighing 50.0 N rests against a
smooth vertical wall as in the figure to the right. If the ladder is just
on the verge of slipping when it makes a 50.0o angle with the
ground, find the coefficient of static friction between the ladder and
the ground.
(a) 0.5
->(b) 0.4
(c) 0.8
(d) 0.3
(e) 0.6
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Physics 1A Winter 2009: Quiz 5
Version A
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8. Two solid wheels of the same mass and thickness have different radii if the density of the
material they are made of differs. Consider spinning up such a set of two wheels separately via
the same force attached tangentially to their respective rims. Which of the following is correct?
(a) both wheels experience the same angular acceleration.
(b) The wheel with the larger radius experiences the larger angular acceleration.
->(c) The wheel with the larger radius experiences the smaller angular acceleration.
9. Three identical massless rods are each acted on by two or more forces, all perpendicular to
the rods and all equal in magnitude (with a force of magnitude F). Which of the rods is in
static equilibrium? Choose one of the following statements below.
rod 1
F
rod 2
F
rod 3
F
F
F
F
(a) Rod 1.
(b) Rod 2.
(c) Rod 3.
(d) All of these three rods are in static equilibrium.
->(e) None of the three rods are in static equilibrium.
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F
F