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Chapter 7, Rotational Motion and the Law of Gravity
C
HAPTER
7
Conceptual Problems
C1. The Earth’s orbit is closest to the Sun in January and farthest from the Sun in July. When is
the Earth moving the fastest in orbit?
a. Neither January nor July since the orbital speed of the Earth is a constant.
b. January
c. July
d. This occurs twice a year, in April and in October.
C2. Two objects are in circular orbits of different radii around the Sun. Which object has the
highest orbital speed?
a. The one closest to the Sun.
b. The one farthest from the Sun.
c. Once in orbit around the Sun, all objects have the same orbital speed regardless of
distance from the Sun. It is the greater radius and greater resulting circumference that
causes the object farther from the Sun to take longer to complete an orbit.
d. This cannot be found without knowing the relative masses of the objects.
C3. For a point on a spinning disc in uniform circular motion, which of the following is not
constant?
a. Its angular speed.
b. Its angular acceleration.
c. Its centripetal acceleration.
d. The magnitude of its total acceleration.
C4. Two points on a merrygoround are located at distances from the center
r
1
and
r
2
, where
r
1
<
r
2
. While the merrygoround is in the process of speeding up to operational speed, which of
the following equations involving magnitudes of angular speed, angular acceleration, and
tangential speed for these points is incorrect?
a.
ω
1
=
ω
2
b.
α
1
=
α
2
c.
v
t
1
=
v
t
2
d. All of the equations are correct.
C5. A car is going around a racetrack at constant speed. The curves around the track have
different radii. In which turn is the magnitude of the car’s acceleration the greatest?
a. It is the greatest in the turn with the greatest radius.
b. It is the greatest in the turn with the smallest radius.
c. The acceleration is zero everywhere because of the constant speed.
d. More information is needed to determine the answer.
93
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7.1 Angular Speed and Angular Acceleration
1.
2 600 rev/min is equivalent to which of the following?
a. 2600 rad/s
b. 43.3 rad/s
c. 273 rad/s
d. 60 rad/s
2.
A grindstone spinning at the rate of 8.3 rev/s has what approximate angular speed?
a. 3.2 rad/s
b. 26 rad/s
c. 52 rad/s
d. 81 rad/s
3.
A 0.12mradius grinding wheel takes 5.5 s to speed up from 2.0 rad/s to 11.0 rad/s. What is
the wheel’s average angular acceleration?
a. 9.6 rad/s
2
b. 4.8 rad/s
2
c. 1.6 rad/s
2
d. 0.33 rad/s
2
4.
What is the angular speed about the rotational axis of the Earth for a person standing on the
surface?
a. 7.3
×
10

5
rad/s
b. 3.6
×
10

5
rad/s
c. 6.28
×
10

5
rad/s
d. 3.14
×
10

5
rad/s
5.
A spool of thread has an average radius of 1.00 cm. If the spool contains 62.8 m of thread,
how many turns of thread are on the spool?
“Average radius” allows us to not need to treat
the layering of threads on lower layers.
a. 100
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 Spring '09
 COFFIN
 Gravity

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