Download Physics Concept Review-1 Key

Physics Concept Review Key
1. What are the SI base units for length, mass, and time?
Length = meter (m), Mass = kilogram (kg), Time = second (s)
2.
2. What quantity describes the difference between an object’s initial position and the object’s final position?
Displacement
3. What is the ratio of an object’s displacement to the time interval during which the displacement occurred?
Velocity
4. Explain how a dog that has moved can have a displacement of zero.
Moves in a circle and ends in the same position it started. Since displacement is the final position minus the initial
position and position did not change. The overall displacement is zero.
5. Construct a graph of position versus time for the motion of a dog, using the data in the table below. What is the dog’s
average velocity? Determine the slope and equation for the graph. Show all work and units.
Displacement (m)
5
4
3
2
1
Linear equation is y = mx + b
m = slope = rise / run = (5-1) / (10-2) = 0.5 m/s
b = y-intercept = 0
y = 0.5x
Displacement = 0.5 * time
2
4
6
8
Time (s)
10
Displacement (m)
6. Construct a graph of position versus time of a jogger, using the data in the table below. Explain how the graph indicates that the jogger’s speed is constant.
6
4
2
The graph shows that the slope is
constant. The slope on a position
vs. time graph is the velocity.
Since the slope is constant, the
velocity must be constant.
7. How can you determine the instantaneous velocity at a given point on a position versus time graph?
Slope
8. A motorized scooter starts from rest and accelerates for 4 s at 2 m/s .
It continues at a constant speed for 6 s. Graph the scooter’s velocity
versus time. What is the scooter’s average velocity for the interval 0–
4 s?
Velocity (m/s)
8
6
4
Average velocity = 4 m/s
2
2
4
6
8
Time (s)
10
9. What is free fall? Any object in motion where gravity is
the only force acting on it.
10. What is the magnitude of the acceleration of an object in free fall near Earth’s surface?
9.8 m/s2
11. Compare the acceleration of a rock in free fall with the acceleration of another rock in free fall dropped a few moments before.
Same
12. The figure above shows the path of a ball tossed from a building. Air resistance is ignored.
a. In the figure above, what would happen to the width of the ball’s path if it were launched with a greater
velocity?
Path width would be greater with a greater starting velocity
b. In the figure above, what would happen to the height of the ball’s path if it were launched with a greater
velocity?
Max height would be greater with a greater starting velocity
13. Describe the graph of the horizontal component of velocity versus time for the motion of the ball shown in the figure
above.
The horizontal component of the velocity does not change because there are no forces in the horizontal direction to
change it.
14. Describe the graph of the vertical component of velocity versus time for the motion of the ball shown in the figure
above. Identify any constants that would appear in the graph.
The vertical component (vy) starts with a high positive value and then gets smaller positive until it reaches the maximum height where vy is zero. Then vy starts becoming larger and larger negative value. The overall rate of change
is negative and represents the negative acceleration that is occurring during the free fall of the projectile.
15. How are force vectors represented in force diagrams?
Arrows.
16. The length of the force vector is proportional to what property of a force?
Magnitude.
17. Construct a free-body diagram of a car being towed.
Fnorm
Ffric
Fapp
Fgrav
18. State Newton’s first law of motion.
An object at rest stays at rest and an object in motion stays in motion with the same velocity unless acted upon by
an unbalanced force. Also called the law of inertia.
19. What happens to an object in motion when it experiences a nonzero net external force?
It accelerates in the direction of the net force.
20. What term is used to describe the vector sum of all the forces acting on an object?
Net force.
21. In the equation form of Newton’s second law, F = ma, what does F represent?
Sum of all forces or net force.
22. Why does it require much less force to accelerate a low-mass object than it does to accelerate a high-mass object the
same amount?
F = ma, so a = F/m. Acceleration and mass are inversely related. As mass decreases, acceleration increases.
23. Distinguish between mass and weight.
Mass is the amount of inertia an object has. Weight is the force of gravity.
24. How does the coefficient of static friction for two surfaces in contact compare to the coefficient of kinetic friction for
the same two surfaces?
Coefficient of static friction is always higher than the coefficient of kinetic friction.
25. Air exerts a force on a leaf as it falls from a tree to Earth. Is the work done on the leaf positive, negative, or zero?
Negative
26. What form of energy is associated with the position of an object in Earth’s gravitational field?
Potential Energy
27. What form of energy is stored in any stretched or compressed object?
Potential Energy
28. State, in words, the work-kinetic energy theorem.
The work done on an object by a net force equals the change in kinetic energy of the object.
29. What quantity is the sum of the kinetic energy and all forms of potential energy in a system?
Total mechanical energy
30. Explain how energy, time, and power are related.
Power is the amount of energy used per unit time.
31. As a bullet travels through the air, it slows down due to air resistance. How does the bullet’s momentum change as a
result?
Momentum goes down as the object slows down because momentum = mass · velocity
32. How can a small force produce a large change in momentum?
It can act for a long time or act on an object with very low mass.
33. What is a term for the quantity Ft, where F is an applied force and t is the time interval over which the force is applied?
Impulse
34. A large moving ball collides with a small stationary ball. Describe how the momentum of each ball changes.
The total momentum of the two balls will stay the same. However much momentum is added to the small ball must
be removed from the large ball.
35. State, in words, the law of conservation of momentum for an isolated system.
The total momentum of objects in a system before a collision equals the total momentum after the collision.
36. Two objects move separately after colliding, and both the total momentum and total kinetic energy remain constant.
Identify the type of collision (elastic or inelastic).
Elastic
37. Two objects stick together and move with the same velocity after colliding. Identify the type of collision (elastic or
inelastic).
Inelastic
38. After colliding, objects are deformed and lose some kinetic energy. Identify the type of collision.
Inelastic
39. What provides the centripetal force for a ball whirled on a string?
Tension
40. Is there an outward force in circular motion? Explain.
No. Inertia makes objects press against the outside surface of the turning object.
41. What provides the centripetal force for the moon’s orbit around Earth?
Force of gravity between the earth and moon.
42. Compare the gravitational force the sun exerts on Earth to the gravitational force Earth exerts on the sun.
Same
43. In the equation for Hooke’s Law, F = –kx, the term k represents the spring constant of a spring.
44. The velocity of the bob on a swinging pendulum reaches a maximum when the bob is in the down position.
45. At what position of an oscillating mass-spring system does the kinetic energy of the mass reach a maximum?
Middle or the equilibrium position.
46. How is the relationship between period and frequency represented as an equation?
f=1/T
47. Electromagnetic waves can move through empty space, but mechanical waves require a medium through which to
travel.
48. Suppose longitudinal waves are generated in a long spring. Describe the motion of a particle within the spring.
The particles move back and forth parallel to the direction the wave is moving.
49. Describe the motion of a particle in a rope through which a transverse wave is passing.
The particles move up and down perpendicular to the direction the wave is moving.
50. In the waveform shown above, which feature of a wave does letter D represent? Amplitude
51. In the transverse waveform shown above, the feature designated by letter B corresponds to a(n) rarefaction in a longitudinal wave.
52. What feature of a wave increases when the source of vibration increases in energy? Amplitude
53. Why is it possible for two waves passing through a medium to occupy the same space at the same time?
The wave is just energy in motion.
54. When two waves meet, they combine according to the superposition principle.
55. A student observes two pulses on a rope wave meet and temporarily form a wave with a greater amplitude than either
of the two waves alone. The student has observed an example of constructive interference.
56. The region of a sound wave in which air molecules are pushed closer together is called a(n) compression.
57. Unlike a transverse wave on a rope, sound travels as a(n) longitudinal wave.
58. Each trough of a sine wave used to represent a sound wave corresponds to a(n) rarefaction of the sound wave.
59. The frequency of a musical sound determines its pitch.
60. In general, does sound travel faster in a gas or in a solid? Explain.
Solid. Sound waves require particles to transfer energy via collisions with neighboring particles. The particles in a
solid are closer together than a gas so the collisions happen faster.
61. Compare the pitch of a sound source moving toward a stationary observer with the pitch of the sound the observer
hears. Explain how this phenomenon occurs.
The pitch will be higher if the sound source is moving towards the observer. This happens because the waves get
closer together.
62. If a light ray strikes a flat mirror with an angle of incidence equal to
, what is the angle of reflection? Explain.
52 degrees. The law of reflection says the angle of incidence equals the angle of reflectance.
63. When does refraction occur?
When light travels from one medium to another.
64. What happens to the speed of light as it moves into a substance with a higher index of refraction?
Slows down.
65. What are the two features of light that change when light moves from one transparent medium into another transparent medium?
Speed, wavelength
66. An object that has a negative electric charge has an abundance of atomic particles called electrons.
67. When an object loses electrons, it acquires a(n) positive electric charge.
68. Materials, such as glass, in which electric charges do not move freely, are called electrical insulators.
69. How does the electric force between two charged objects change when the distance between the two objects is doubled? Explain.
Decreases by 4X. Felec is inversely proportional the distance squared. Felec = kq1q2 / r2
70. What is electric force?
The force caused on an electrically charged object by the presence of an electrically charged object.
71. How are gravitational and electric force alike?
They are both inversely proportional to the distance between the objects squared.
72. How are gravitational force and electric force different?
Gravitational force is always attractive while electrical force can be attractive or repulsive.
73. Draw the lines of force representing the electric field surrounding two objects that have equal magnitude charges of
opposite polarity.
74. In the figure shown at left, why do only half of the lines originating from the positive
charge terminate on the negative charge?
The positive charge has twice the magnitude of the negative charge.
75. Is the charge shown in the figure at right positive or negative? How about the figure on the right side?
positive
negative
76. The space around a charged object contains an electric field.
77. What is electrical potential energy?
Electric potential energy is a potential energy (measured in joules) that results from electric forces
78. Electrical potential energy is a result of what interaction?
Interaction between charged particles.
79. What is electric potential?
Voltage
80. What is potential difference?
The difference in electrical potential between two points.
81. What is the source of the energy produced by a battery?
Chemical reaction
82. What is electric current?
The amount of charge moving per time (Coulombs / second or C/s which is equal to Amperes or A)
83. Identify the types of elements in the schematic diagram above and the number of each type.
2 batteries or power supplies, 3 resistors.
84. Draw a schematic diagram that contains a 1000 V battery, a 3000  resistor, and an open switch wired as a series circuit.
85. Current does not flow through the circuit shown in the schematic
diagram above. Explain why this is so.
The switch is open.
86. Which bulb or bulbs will have a current in the schematic diagram
shown above?
Just A
87.
How does the equivalent resistance of a series circuit compare to the resistance values of the individual resistances in the circuit?
The equivalent resistance is the sum of the individual resistances, so equivalent resistance will always be greater than any one single resistor’s resistance.
88.
How does the equivalent resistance of a parallel circuit compare to the resistance values of the individual resistances in the circuit?
The equivalent resistance will always be less than the smallest resistor resistance in parallel.
89.
You have seven resistors available, and all of the resistors have a value of 100.0 . How would you connect these
seven resistors to produce an equivalent resistance of 70.0 ?
Yikes. Nothing this hard will be on the NCFE. Good luck guys, it has been a pleasure teaching you.
–Mr. Hampton