Basic Physics Content with Answers
1.
In the absence of air resistance, a ball of mass
m is tossed upward to reach a height
of 20 m. At the 10m position, half way up, the net force on the ball is
A. 2mg. B.
mg. C.
mg/2. D. mg/4.
B. is correct, as a vector diagram would show.
Other choices show carelessness or confusion between force and speed, and what
constant acceleration means.
2.
When you drop a ball it accelerates downward at
9.8 m/s2. If you instead throw it downward, then its acceleration
immediately after leaving your hand, assuming no air resistance, is A. 9.8 m/s2.
B. more
than 9.8 m/s2.
C. less
than 9.8 m/s2.
D. Cannot
say, unless the speed of throw is given.
A. is correct. Choices B and D indicate
confusion between speed and acceleration.
3.
A heavy rock and a light rock in free fall (zero
air resistance) have the same acceleration. The reason the heavy rock doesn’t
have a greater acceleration is that the A. force due to gravity is the same on
each.
B. air
resistance is always zero in free fall.
C. inertia
of both rocks is the same.
D. ratio
of force to mass is the same.
E.
None of these.
D is correct. Choices A and C indicate
confusion about Newton’s second law. Choice B, although a true statement,
evades the reason, and is therefore not the best answer.
4.
A cannonball is fired horizontally at 10 m/s
from a cliff. Its speed one second after being fired is about
A. 10
m/s. B. 14 m/s. C. 16 m/s. D. 20 m/s.
B. is correct, as vector addition shows if a
student knows that gain of vertical speed in 1 s is 10 m/s. Choice a gives the
horizontal or vertical speed, but not the resultant speed. Choice C has no
credibility, and choice D
indicates scalar addition of two 10 m/s
vectors.
5.
Relative to the ground, an airplane gains speed
when it encounters wind from behind, and loses speed when it encounters wind
head on. When it encounters wind at a right angle to the direction it is
pointing, its speed relative to the ground below
A. increases.
C. is the same as if there were no
wind.
B. decreases.
D. Need more information.
A is correct. Choice B has no credibility.
Choice C shows a lack of applying vectors to this situation.
6.
A karate chop delivers a force of 3000 N to a
board that breaks. The force that the board exerts on the hand during this
event is
A. less
than 3000 N. C. greater than
3000 N.
B. 3000
N. D. Need more information.
B is correct. Other choices bypass the
essential physics here—Newton’s third law.
7.
A math book and a physics book are tied together
with a length of string. With the string taut, one book is pushed off the edge
of a table. As it falls, the other book is dragged horizontally across the
table surface. With no friction, acceleration of the books is A. zero.
B. g/2.
C. g.
D. a
value between zero and g.
E.
a value that could be greater than g.
D is correct. Choice B is true only for
equal masses, an unjustified assumption since the books are different from each
other. Choices A and E are incorrect
8.
When an increase in speed doubles the momentum
of a moving body, its kinetic energy A. increases, but less than doubles. C. more than doubles.
B.
doubles. D.
depends on factors not stated.
C is correct. Choice B would be correct if KE,
like momentum, were directly proportional to speed. Choices A and
D are likely guesses.
9.
When an increase in speed doubles the kinetic
energy of a moving body, its momentum A. increases, but less than doubles. C. more than doubles.
B.
doubles. D.
depends on factors not stated.
A. is correct. Other choices don’t properly
distinguish between the linear speed dependence of momentum and the squaring of
speed for KE.
10. Big
brother and little sister can balance on a seesaw because of balanced
A. forces.
B. torques. C. energies. D. All of these.
B. is correct. Choice A has some credibility if
all forces are taken into account. Choice C would be relevant if the children
are going up or down, leaving B as the best answer.
11. When
a spinning system contracts in the absence of an external torque, its
rotational speed increases and its angular momentum
A. decreases.
C. remains unchanged.
B. increases.
D. may increase or decrease.
C. is correct. Other choices miss the essential
physics here—the conservation of angular momentum.
12. Consider
a ball rolling down an inclined plane. The normal force on the ball (the force
perpendicular to the plane).
A. is
mg. C.
may be greater or less than mg.
B. is
greater than mg, always. D. is less than mg, always.
D is correct, as a free-body diagram would
show. Other choices indicate a weakness in force analysis via freebody
diagrams.
13. Consider
a ball rolling in a horizontal circular path on the inside surface of a cone.
The normal force on the ball
A. is
mg. C.
may be greater or less than mg.
B. is
greater than mg, always. D. is less than mg, always.
B is correct, as a free-body diagram would
clearly show that the normal vector has a greater magnitude than its vertical
component (magnitude mg). Magnitude of the normal vector is also greater than
the horizontal component, the net force directed to the center of circular
motion. Other choices show a weakness in force analysis via free-body diagrams.
14. When
a ball at rest hangs by a single vertical string, tension in the string is mg. If the ball is made to move in a
horizontal circle so that the string describes a cone, string tension A. is mg.
B. is
greater than mg, always.
C. is
less than mg, always.
D. may
be greater or less than mg depending
on the speed of the ball.
B is correct. Similar to the preceding
question, a free-body diagram clearly shows the tension vector has a greater
magnitude than that of its vertical component, mg. Again, other choices show a
weakness in force analysis via free-body diagrams.
15. Imagine
you're standing on the surface of a shrinking planet. If it shrinks to
one-tenth its original diameter with no change in mass, on the shrunken surface
you'd weigh
A. 1/100
as much. C. 100 times as
much. E. None of these.
B. 10
times as much. D. 1000 times as
much.
C. is correct, as analysis of Newton’s equation
for the law of gravitation would show. Choice A indicates confusion, and choice
B misses the inverse -square law. Choices D and E likely indicate
carelessness or a guess.
16. The
fact that the Moon always shows its same face to Earth is evidence that the
Moon rotates about its axis about once per A. day.
B. month.
C. year.
D. None
of these, for the moon does not rotate about an axis.
B is correct. Choice D highlights a common
misconception to be addressed.
17. The
Moon is most responsible for Earth’s tides. Which pulls more strongly on the
Earth and its oceans?
A. Moon.
B. Sun. C. Both about equally.
B. is correct. Choice A indicates the student
misses the distinction between force and differences in force, the crux of
tides. Choice C is incorrect.
18. A
spacecraft on its way from Earth to the Moon is pulled equally by Earth and
Moon when it is A. closer to the Earth’s surface.
B. closer
to the Moon’s surface.
C. half
way from Earth to Moon.
D. At
no point, since Earth always pulls more strongly.
B is correct. Choice a indicates confusion
about the role of mass or distance, choice C disregards the inversesquare law,
and choice D disregards the law of universal gravitation.
19. Earth
satellites such as the Space Shuttle orbit at altitudes that are above the
Earth’s
A. atmosphere.
B. gravitational field. C. Both of these.
A is correct. Choice C, a popular incorrect
answer, highlights a major misconception about the extent of Earth’s
gravitational field—one to be addressed.
20. The
mass of a classical atom comes mostly from its ____ ; and its volume from its
______.
A. nucleons;
nucleons. C. electrons; nucleons.
B. electrons;
electrons. D. nucleons; electrons.
D is correct. Other choices are likely
guesses without merit.
21. Consider
a block of wood floating on water. If you push down on the top of the block
until it’s completely submerged, the buoyant force on it A. increases.
B. decreases.
C. remains
the same.
D. depends
on how far beneath the water surface it is pushed.
A. is correct. Other choices indicate a missed
connection between greater buoyant force and greater amount of displaced water.
22. An
inflated balloon with a heavy rock tied to it submerges in water. As the
balloon sinks deeper and deeper, the buoyant force acting on it
A. increases.
C. remains largely unchanged.
B. decreases.
D. Need more information.
B is correct. Other choices indicate failure
to see that the balloon is compressed by water pressure—and compression is
greater with greater depth—displacing less water. Because of multiple concepts,
expect a large number of incorrect answers.
23. The
principal source of the Earth’s internal energy is
A. tidal
friction. C. radioactivity.
B. gravitational
pressure. D. geothermal heat.
C. is correct (as missed by Lord Kelvin in
calculating the age of the Earth before radioactivity was known). Choices A and
B are smaller sources, and choice D explains nothing.
24. The
surface of Planet Earth loses energy to outer space due mostly to
A. conduction.
B. convection. C. radiation. D.
radioactivity.
C is correct, for it is the only choice that
takes the vacuum of outer space into account. Other choices don’t.
25. The
"greenhouse gases" that contribute to global warming absorb
A. more
visible radiation than infrared. C.
visible and infrared about equally.
B. more
infrared radiation than visible. D.
very little radiation of any kind.
B is correct. Choice A has the facts
backward. Choices C and D are without merit.
26. In
a mixture of hydrogen, oxygen, and nitrogen gases at a given temperature, the
molecules having the greatest average speed are those of A. hydrogen.
B. oxygen.
C. nitrogen.
D. But
all have the same speed on average.
A. is correct. Other choices either don’t acknowledge
hydrogen’s smallest mass, or that for the same KE, smaller mass means greater
speed—or fail to see the relationship between temperature and KE.
27. The
electrical force of attraction between an electron and a proton is greater on
the A. proton.
B. electron.
C. Neither;
both are the same.
C is correct. Other choices don’t consider
Newton’s third law.
28. Immediately
after two separated charged particles are released from rest, both increase in
speed. The particles therefore have
A. the
same sign of charge.
B. opposite
signs of charge.
C. either
the same or opposite signs of charge.
D. Need
more information.
C is correct. Choice A is likely a too-hasty
response. Choice B would be correct if increase of acceleration rather than
speed were the case. Choice D has no merit.
29. Compared
with the current in the white-hot filament of a common lamp, the current in the
connecting wire is
A. less.
C. the same.
B. more.
D. Need more information.
C. is correct. Other choices indicate a common
misconception about current, which should be addressed.
30. As
more lamps are connected in a series circuit, the current in the power source
A. increases.
C. remains much the same. B.
decreases. D. Need more information.
B. is correct. Other choices indicate weakness
in Ohm’s law in circuitry.
31. As
more lamps are connected in parallel in a circuit, the current in the power
source
A. increases.
C. remains much the same. B.
decreases. D. Need more information.
A is
correct. More challenging than the previous question, other choices also
indicate weakness in Ohm’s law in circuitry.
32. A
capacitor loses half its charge every second. If after five seconds its charge
is q, what was its initial charge?
A. 4q. C.
16q. E.
None of these.
B. 8q. D.
32q.
D is correct. Not noting the exponential
nature of decay likely accounts for other choices. Miscalculation may account
for choices C or E.
33. The
magnetic force on a moving charged particle can change the particle’s
A. speed.
B. direction. C. Both of these. D. Neither of these.
B. is correct. Choices A or C may indicate
confusion between electric and magnetic forces on particles.
34. A
step-up transformer in an electrical circuit can step up
A. voltage.
B. energy. C. Both of these. D. Neither of these.
A is correct. Choice B seriously violates
the conservation of energy, as does choice C—a call for serious remedy.
35. The
mutual induction of electric and magnetic fields can produce
A. light.
B. energy. C. Both of these. D.
Neither of these.
A is correct. A wrong answer here,
especially if it follows a wrong answer in the preceding question, calls for
serious remedy.
36. All
of the following are electromagnetic waves EXCEPT A. radio waves. B.
microwaves.
C. light
waves.
D. X-rays.
E.
None is outside the family; all are
electromagnetic waves.
E is correct. Choice A indicates confusion
between sound and radio waves. Other choices indicate ignorance of the
electromagnetic spectrum.
37. You
swing to and fro on a playground swing. If you stand rather than sit, the time
for a to-and-fro swing is
A. lengthened.
B. shortened. C. unchanged.
B. is correct, since center of gravity is
higher and effectively shortens pendulum length. Other choices indicate
incorrect assessment of pendulum motion.
38. Compared
with the sound you hear from the siren of a stationary fire engine, the sound
you hear when it approaches you has an increased
A. speed.
B. frequency. C. Both of these. D. Neither of these.
B. is correct. Choice A indicates ignorance of
the Doppler effect, and choice C confusion rather than ignorance.
39. During
the time an aircraft produces a sonic boom, the aircraft is
A. breaking
the sound barrier. C. flying
faster than sound.
B. pulling
out of a subsonic dive. D. Each of
these produces a sonic boom.
C. is correct. Choice A illustrates the popular
misconception that the boom occurs only when a craft exceeds the speed of
sound. Choice C is the general and therefore best answer. Choice B is incorrect
due to its subsonic speed, which could be confused for supersonic speed, in
which case d might seem to be correct
40. The
phenomenon of interference occurs for
A. sound
waves. B. light waves. C. Both of these. D. Neither of these.
C is correct. Other choices fail to
recognize this characteristic property of waves in general.
41. The
speed of sound in air depends on
A. frequency.
D. All of these.
B. wavelength.
E. None of these.
C. air
temperature.
C is correct. Other choices indicate basic
misconceptions about sound waves.
42. Your
friend states that under all conditions, any radio wave travels faster than any
sound wave. You
A. agree
with your friend. B.
disagree with your friend.
A is correct. Choice B, if not a guess, may
indicate “all conditions” as simply too big to buy into.
43. The
phenomenon of beats results from sound
A. reflection.
D. All of these.
B. refraction.
E. None of these.
C. interference.
C is correct. Other choices indicate little
or no understanding of beats.
44. To
view your full-face image in a steamy mirror, compared to the height of your
face, the minimum height of the patch to wipe away is A. one-quarter.
B. one-half.
C. the
same.
D. dependent
on your distance from the mirror.
B is correct. Choice D, which may be the
answer of most students, highlights a widely held misconception about mirrors
and reflection. Choices A and C are likely guesses.
45. Light
reflecting from a smooth surface undergoes a change in
A. frequency.
D. All of these.
B. speed.
E. None of these.
C. wavelength.
E is correct. Other choices indicate a wild
guess, or ignorance about reflection.
46. Which
of these changes when light refracts in passing from one medium to another?
A. Speed.
B. Wavelength. C. Both of these. D. Neither of these.
C is correct. Choice A may be a popular
answer, but fails to account for the compression of waves at reduced speed.
Students need to know that frequency does not change
47. When
white light passes through a prism, green light is bent more than
A. blue
light. D. Two of these choices are
correct.
B. violet
light. E. None of these choices is
correct.
C. red
light.
C is correct. Other choices indicate
ignorance of fact that a prism refracts higher frequencies more than lower
frequencies, or uncertainty about the relative frequencies of different colors.
48. When
you look at the red petals of a rose, the color light you're seeing is
A. red.
D. a mixture of green and yellow.
B. green.
E. cyan.
C. white
minus red.
A is correct. Other choices illustrate the
adage that a little knowledge can often be more harmful than none. This is a
no-brainer for children, but can be confusing to those who expect complexity
where there is none.
49. When
the color yellow is seen on your TV screen, the phosphors being activated on
the screen are
A. mainly
yellow. C. green and
yellow.
B. blue
and red. D. red and green.
D is correct. Other choices indicate
weakness in the rules of color addition.
50. The
red glow in the neon tube of an advertising sign is a result of
A. fluorescence.
C. polarization. E. de-excitation.
B. incandescence.
D. coherence.
E is correct. Other choices are likely
guesses, for none have merit.
51. Polarization
is a property of
A. transverse
waves. C. all waves.
B. longitudinal
waves. D. None of these.
A is correct. Other choices indicate lack of
knowledge that polarization distinguishes between transverse and longitudinal
waves.
52. Astrophysicists
are able to identify the elements in the outer layers of a star by studying its
A. Doppler
effect. C. temperature.
B. molecular
structure. D. spectrum.
D is correct. Other choices are likely
guesses.
53. If
the Sun collapsed to become a black hole, Planet Earth would
A. continue
in its present orbit. D. be pulled
apart by tidal forces.
B. fly
off in a tangent path. E.
Both C and D.
C. likely
be sucked into the black hole.
A is correct, as no values change in
Newton’s formula for gravitation. Other choices support common misconceptions,
a signal for remedial work in class.
54. Any
atom that emits an alpha particle or beta particle A. becomes an atom of a
different element, always.
B. may
become an atom of a different element.
C. becomes
a different isotope of the same element.
D. increases
its mass.
A. is correct. Other choices indicate poor understanding
of radioactivity.
55. Suppose
the number of neutrons in a reactor that is starting up doubles each minute,
reaching one billion neutrons in 10 minutes. When did the number of neutrons
reach half a billion?
A. 1
minute. C. 5 minutes. E. None of these.
B. 2
minutes. D. 9 minutes.
D is correct. Other choices indicate a
misunderstanding of exponential growth, or a miscalculation of such.
56. When
a uranium nucleus undergoes fission, the energy released is primarily in the
form of
A. gamma
radiation. C. kinetic energy of
ejected neutrons.
B. kinetic
energy of fission fragments. D.
All of these about equally.
B is correct. Choice A supports a popular
misconception of gamma radiation in fission. Choice C may be influenced by the
large amount of energy of neutrons in fusion reactions, whereby only two
particles share energy. Choice D is likely a guess.
57. When
a fusion reaction converts a pair of hydrogen isotopes to an alpha particle and
a neutron, most of the energy released is in the form of
A. gamma
radiation. C. kinetic energy of
the neutron.
B. kinetic
energy of the alpha particle. D.
All of these about equally.
C. is correct, in accord with momentum
conservation. Choice A supports the same popular misconception of gamma
radiation in fission. Choice B may indicate confusion with fission —or is a guess, as choice D likely is.
58. Because
there is an upper limit on the speed of particles, there is also an upper limit
on
A. momentum.
C. temperature. E. None of these.
B. kinetic
energy. D. All of these.
E is correct, for momentum and kinetic
energy (and, potentially, temperature) approach infinity as speed approaches
the speed of light.
59. Relativistic
equations for time dilation, length contraction, and relativistic momentum and
energy hold true at
A. speeds
near that of light. C. all
speeds.
B. everyday
low speeds. D. only approximately.
C is correct. Choice A is based on the
misconception that relativity holds only at high speeds. It also holds at low
speeds where it duplicates classical predictions.
60.
The equation E = mc2 indicates that energy
A. equals
mass moving at the speed of light squared.
B. equals
moving mass.
C. is
fundamentally different than mass.
D. and
mass are closely related.
D is correct. Choice A indicates misreading of
the formula, and choices B and C are without merit.
