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Chapter 7 Study Questions w/ MC
Short Answer Questions Section 7-1 and Appendix J
Measuring Rotation and Centripetal Force
1. What units must be used for
&
in the rotational kinematic equations found in table 2 on
page 901 (H2009)? How are period ( ) and cycles per second (Hertz) related to
(from class
notes)?
2. How are angular speed and tangential speed related ? (See appendix J, page 902 of H2009)
3. A. Explain how an object moving at a constant speed can have a nonzero acceleration.
B. Explain how to subtract two velocity vectors going in different (but not opposite) directions. Use
the terminology:
and
. Use a diagram to illustrate.
C. (H) Show the direction of the nonzero acceleration by using the vector operations for determining
. Why is
in the same direction as the nonzero acceleration?
4. Two horses are side by side on a carousel. Which has a greater tangential speed—the one closer
to the center or the one further from the center? Explain using the equation on page 902.
5. What provides the centripetal force for a car driving on a circular track?
6. What provides the centripetal force for a ball whirled on a string?
7. Show how the equation for centripetal force can be derived by substituting the equation for
centripetal acceleration into Newton’s second law.
8. Is there an outward force in circular motion? Explain.
9. A ball is whirled in a horizontal circular path on the end of a string. Predict the path of the ball when
the string breaks. Explain your answer using Newton’s 1st and 2nd laws.
Problems Section 7-1 and Appendix
Measuring Rotation and Centripetal Force
10. A 35 kg child moves with uniform circular motion while riding a horse on a carousel. The horse is
3.2 m from the carousel’s axis of rotation and has a tangential speed of 2.6 m/s.
A. What is the child’s centripetal acceleration?
B. What is the centripetal force on the child?
11. A car on a roller coaster loaded with passengers has a mass of 2.010 kg. At the lowest point of
the track, its radius of curvature is 24 m and the roller car has a tangential speed of 17 m/s.
A. What is the centripetal acceleration of the roller coaster car at the lowest point on the track?
B. What centripetal force is exerted on the roller coaster car at the lowest point?
12. An 18.5 kg child sits 1.5 m from the center of a spinning merry-go-round.
A. If the merry-go-round were to rotate at 0.10 Hz, what is the centripetal force acting on the child to
maintain her circular motion?
B. (H) If the child were not holding on, and
, would she slide off or stay put?
13. Tarzan tries to cross a river by swinging from one bank to the other on a vine 10.0 m long. His
speed at the bottom of his swing is 8.0 m/s. Tarzan does not know that the vine has a breaking
strength of
N. What is the largest mass Tarzan can have and still make it across the
river?
(from # 11 page 263 Holt 2009)
14. A satellite in a circular orbit experiences a centripetal acceleration of 8.62 m/s . The tangential
speed of the satellite is 7.65  10 m/s. What is the altitude of the satellite? (r = 6.38  10 m)
Long Open Response Questions Section 7-1 and Appendix
Measuring Rotation and Centripetal Force
15. Because of Earth’s rotation, you would weigh slightly less at the equator than at the poles, why is
this so? (H) How fast would the Earth have to rotate in order to cancel out your (apparent) weight?
Short Answer Questions Section 7-2
Newton’s Law of Gravitation
16. What provides the centripetal force for the moon’s orbit around Earth?
17. Describe how the moon causes tides on Earth. Why are there 2 tides per day and not 1?
18. Compare the
the Sun exerts on Earth to the
Earth exerts on the Sun.
19. Earth exerts a 1.0 N gravitational force on an apple.
A. Does the apple accelerate toward Earth, or does Earth accelerate toward the apple? Explain.
B. What is the magnitude of the gravitational force the apple exerts on Earth?
C. What is Earth’s weight in the apple’s gravitational field?
Problems Section 7-2
Newton’s Law of Gravitation
20. What forces would a 67.5 kg person experience if he were to stand (at different times) on Earth,
Mars and Pluto?
Planet
m
r
Earth
5.98 X 1024 kg
6.37 X 106 m
Mars
6.34 X 1023 kg
3.43 X 106 m
21
Pluto
5 X 10 kg
4 X 105 m
21. A planet has twice the mass of Earth. How much larger would the radius of the planet have to be for
the gravitational field strength, g, at the planet’s surface to be the same as on Earth’s surface?
Short Answer Questions Section 7-3 and Appendix
Kepler’s Laws and Planetary Motion
22. What is Kepler’s first law of planetary motion?
23. What is Kepler’s second law of planetary motion?
24. State Kepler’s third law of planetary motion, both in words and symbolically.
25. What term describes change in tangential speed of a rotating object? (See appendix of H2009)
26. In an elliptical orbit, a satellite does not maintain a constant tangential speed (
). Describe
where in such an orbit
is positive and where
is negative. (Activity “the orbit”, chapter 8,
Glencoe; see #44 below)
27. Sketch an elliptical satellite or planetary orbit and show the approximate
for four positions within the orbit. (Activity “the orbit”)
and
components
28. On what variable factors do the period and speed of an object in circular orbit depend? (Activity “the
orbit”)
29. What law does the diagram shown above illustrate?
Problem Section 7-3 and Appendix
Kepler’s Laws and Planetary Motion
30. A new moon is discovered orbiting Neptune with an orbital speed of 9.3  10 m/s. Neptune’s mass
is 1.0  10 kg. What is the radius of the new moon’s orbit? What is the orbital period? Assume
that the orbit is circular. (G = 6.673  10
Nm /kg )
Long Open Response Question Section 7-3 and Appendix
Kepler’s Laws and Planetary Motion
31. (H) Show how the constant of proportionality in Kepler’s third law can be found by equating
gravitational force and the centripetal force in a circular orbit.
Short Answer Questions Section 7-4 and Appendix
Torque and Simple Machines
32. What are the units for “torque”? How are they different from the units for “work”?
33. How will an object move if it is acted on by a nonzero net torque and a net force of zero?
34. According to the sign conventions used in the text, in what direction will an object rotate if the sign
of the net torque on the object is negative? (H) What vector operation is equivalent?
35. Explain how the operation of a simple machine alters the applied force and the distance
(displacement) moved.
36. How does the use of a machine alter the work done on the object?
Problems Section 7-4 and Appendix
Torque and Simple Machines
37. To warm up before a game, a baseball pitcher tosses a 0.15 kg ball by rotating his forearm, which is
0.32 m in length, to accelerate the ball. The ball starts at rest and is thrown at a speed of 12 m/s in
0.40 s. While the ball is in the pitcher’s hand, what torque is applied to the ball to produce the final
tangential speed?
38. A child with a weight of 4.50  10 N sits on a seesaw 0.60 m from the axis of rotation. How far
from the axis of rotation on the other side should a child with a weight of 6.00  10 N sit so the
seesaw will remain balanced?
39. A bucket filled with water has a mass of 23 kg and is attached to a rope wound around a cylinder
with a radius of 0.050 m at the top of a well. What torque does the weight of the water and bucket
produce on the cylinder? (g = 9.81 m/s )
40. A force of 255 N is needed to pull a nail from a wall, using a claw hammer. If the resistance force of
the nail is 3650 N, what is the mechanical advantage of the hammer?
41. A force of 1250 N is needed to move a crate weighing 3270 N up a ramp that is 4.55 m long. If the
elevated end of the ramp is 0.750 m high, what is the efficiency of the ramp?
Chapter 7 Activities and Lab Experiences
42. Design a laboratory experience that investigates the relationship between tangential speed ( ) and
centripetal force (
). Your error analysis will require you to calculate
that value to the measured value for
from
and compare
. Materials and lab space will be provided.
43. Modify problem #13 into a laboratory experience. Materials and lab space will be provided.
Set up a pendulum with slotted masses and a force guage and measure the tension in the
pendulum string. Predict the relationships between mass and string tension, (H) velocity and string
tension, and (H) string length and string tension. Good luck!
44. Draw an eliptical orbit of a planet around a star using 2 pins and a single loop of string. Use
colored pencils to distinguish the various features of the orbit. Attach a calculation sheet. (Use
Glencoe 1999 “orbits” as a guide).
A. Locate the sun on your drawing (K1stL).
B. Locate and label the closest approach to the star (use the correct term).
C. Locate and label the farthest point from the star (use the correct term).
D. Locate 2 other intermediate positions on opposite sides of the orbit from each other.
E. With the
of the farthest point equaling 1cm, determine the magnitude and direction of the
force vectors for each of the 3 other orbital positions.
F. (H) Using the graphical method, break the force vectors of the two intermediate orbital positions
into their tangential ( ) and perpendicular ( ) components.
G. With the
of the farthest point equaling 1 cm, (CPA) estimate and sketch the tangential
velocity vectors for each position. (H) Draw the tangential velocity vectors to scale using a
derivation of Kepler’s 3rd law (see #31 above)
45. Sketch and identify five (5) simple machines as identified in the text. Show in a laboratory setting
the mechanical advantage and (H) efficiency for 2 types of simple machines.
Chapter 7 Multiple Choice Questions
Identify the letter of the choice that best completes the statement or answers the question.
Questions are in order by section.
____ 46. What term describes a change in the speed of an object in circular motion?
a. tangential speed
c. centripetal acceleration
b. tangential acceleration
d. centripetal force
____ 47. What is the term for the net force directed toward the center of an object’s circular path?
a. circular force
c. centripetal force
b. centrifugal force
d. orbital force
____ 48. When a car makes a sharp left turn, what causes the passengers to move toward the right side of
the car?
a. centripetal acceleration
c. centrifugal force
b. centripetal force
d. inertia
____ 49. Why does an astronaut weigh less on the moon than on Earth?
a. The astronaut has less mass on the moon.
b. The astronaut is farther from Earth’s center when he or she is on the moon.
c. The gravitational field strength is less on the moon’s surface than on Earth’s
surface.
d. The astronaut is continually in free fall because the moon orbits Earth.
____ 50. If you lift an apple from the ground to some point above the ground, the gravitational potential
energy in the system increases. This potential energy is stored in
a. the apple.
b. Earth.
c. both the apple and Earth.
d. the gravitational field between Earth and the apple.
____ 51. An object’s tendency to resist acceleration is measured by the object’s
a. gravitational mass.
c. gravitational field strength.
b. inertial mass.
d. weight.
____ 52. In this text, which of the following symbols represents gravitational field strength?
a. F
c. g
b. G
d. F
____ 53. In this text, which of the following symbols represents the constant of universal gravitation?
a. F
c. g
b. G
d. F
____ 54. Which of the following equations expresses Newton’s law of universal gravitation?
a.
c.
b.
d.
____ 55. Two small masses that are 10.0 cm apart attract each other with a force of 10.0 N. When they are
5.0 cm apart, these masses will attract each other with what force?
(G = 6.673  10
Nm /kg )
a. 5.0 N
c. 20.0 N
b. 2.5 N
d. 40.0 N
____ 56. Until the middle of the 16th century, most people believed ____ was at the center of the universe.
a. Earth
c. the sun
b. the moon
d. a black hole
____ 57. The equation for the speed of an object in circular orbit is
____ 58.
____ 59.
____ 60.
____ 61.
____ 62.
____ 63.
____ 64.
. What does m represent in
this equation?
a. the mass of the sun
c. the mass of the central object
b. the mass of Earth
d. the mass of the orbiting object
How would the speed of Earth’s orbit around the sun change if Earth’s distance from the sun
increased by 4 times?
a. It would increase by a factor of 2.
c. It would decrease by a factor of 2.
b. It would increase by a factor of 4.
d. The speed would not change.
How would the speed of Earth’s orbit around the sun change if Earth’s mass increased by 4 times?
a. It would increase by a factor of 2.
c. It would decrease by a factor of 2.
b. It would increase by a factor of 4.
d. The speed would not change.
Which of the following quantities measures the ability of a force to rotate or accelerate an object
around an axis?
a. axis of rotation
c. tangential force
b. lever arm
d. torque
If you cannot exert enough force to loosen a bolt with a wrench, which of the following should you
do?
a. Use a wrench with a longer handle.
b. Tie a rope to the end of the wrench and pull on the rope.
c. Use a wrench with a shorter handle.
d. You should exert a force on the wrench closer to the bolt.
Suppose a doorknob is placed at the center of a door. Compared with a door whose knob is located
at the edge, what amount of force must be applied to this door to produce the torque exerted on the
other door?
a. one-half as much
c. one-fourth as much
b. two times as much
d. four times as much
What kind of simple machine are you using if you pry a nail from a board with the back of a
hammer?
a. a wedge
c. a lever
b. a pulley
d. a screw
A box weighing 210 N is pushed up an inclined plane that is 2.0 m long. A force of 140 N is
required. If the box is lifted 1.0 m, what is the efficiency of the inclined plane?
a. 33%
c. 67%
b. 50%
d. 75%