Transcript Physics 100 Review for Final Exam

Physics 100
Review for Final Exam
Which of these is not a scientific hypothesis?
A. Protons carry an electric charge.
B. Undetectable particles are some of nature’s
secrets.
C. Charged particles bend when in a magnetic
field.
D. All of the above are scientific hypotheses.
Which of these is not a scientific hypothesis?
A. Protons carry an electric charge.
B. Undetectable particles are some of
nature’s secrets.
C. Charged particles bend when in a magnetic
field.
D. All of the above are scientific hypotheses.
Explanation:
Choices A and C can be disproved by experiments.
Choice B has no test for wrongness, so it is not a scientific
hypothesis.
Which of these is a scientific hypothesis?
A. The Moon is made of green cheese.
B. Atomic nuclei are the smallest particles in
nature.
C. A magnet will pick up a copper penny.
D. Cosmic rays cannot penetrate the thickness of
your Conceptual Physics textbook.
Which of these is a scientific hypothesis?
A. The Moon is made of green cheese.
B. Atomic nuclei are the smallest particles in
nature.
C. A magnet will pick up a copper penny.
D. Cosmic rays cannot penetrate the thickness
of your Conceptual Physics textbook.
Explanation:
All are scientific hypotheses!
All have tests for proving wrongness, so they pass the test of
being a scientific hypothesis.
Which of these often changes over time with
further study?
A. Facts.
B. Theories.
C. Both of the above.
D. Neither of the above.
Which of these often changes over time with
further study?
A.
B.
C.
D.
Facts.
Theories.
Both of the above.
Neither of the above.
Explanation:
Both can change. As we learn new information, we refine
our ideas; likewise in science.
A person who says, “that’s only a theory” likely
doesn’t know that a scientific theory is a
A. guess.
B. number of facts.
C. hypothesis of sorts.
D. vast synthesis of well-tested hypotheses and
facts.
A person who says, “that’s only a theory” likely
doesn’t know that a scientific theory is a
A. guess.
B.number of facts.
C.hypothesis of sorts.
D.vast synthesis of well-tested hypotheses
and facts.
Explanation:
The word “theory” in everyday speech is different than its use in science.
In science, only a vast, experimentally verifiable body of knowledge is a theory.
What is the net force acting on the box?
A. 15 N to the left
B. 15 N to the right
C. 5 N to the left
D. 5 N to the right
?
What is the net force acting on the box?
A. 15 N to the left
B. 15 N to the right
C. 5 N to the left
D.5 N to the right
When you stand on two bathroom scales with
one foot on each scale and with your weight
evenly distributed, each scale will read
A. your weight.
B. half your weight.
C. zero.
D. more than your weight.
When you stand on two bathroom scales with
one foot on each scale and with your weight
evenly distributed, each scale will read
A.
B.
C.
D.
your weight.
half your weight.
zero.
more than your weight.
Explanation:
• You are at rest, so F=0.
• Forces from both scales add to cancel your weight.
• Force from each scale is one-half your weight
You are pushing a crate at a constant speed in
a straight line. If the friction force is 75 N,
how much force must you apply?
A. more than 75 N
B. less than 75 N
C. equal to 75 N
D. not enough information
You are pushing a crate at a constant speed in
a straight line. If the friction force is 75 N,
how much force must you apply?
A.
B.
C.
D.
more than 75 N
less than 75 N
equal to 75 N
not enough information
Explanation:
The crate is in dynamic equilibrium, so, F = 0.
Your applied force balances the force of friction.
The average speed of driving 30 km in 1 hour is
the same as the average speed of driving
A. 30 km in 1/2 hour.
B. 30 km in 2 hours.
C. 60 km in 1/2 hour.
D. 60 km in 2 hours.
The average speed of driving 30 km in 1 hour is
the same as the average speed of driving
A.
B.
C.
D.
30 km in 1/2 hour.
30 km in 2 hours.
60 km in 1/2 hour.
60 km in 2 hours.
Explanation:
Average speed = total distance / time
So, average speed = 30 km / 1 h = 30 km/h.
Now, if we drive 60 km in 2 hours:
Average speed = 60 km / 2 h = 30 km/h
Same
An automobile is accelerating when it is
A. slowing down to a stop.
B. rounding a curve at a steady speed.
C. Both of the above.
D. Neither of the above.
An automobile is accelerating when it is
A. slowing down to a stop.
B. rounding a curve at a steady speed.
C. Both of the above.
D. Neither of the above.
Explanation:
• Change in speed (increase or decrease) is acceleration,
so slowing is acceleration.
• Change in direction is acceleration (even if speed stays
the same), so rounding a curve is acceleration.
Acceleration and velocity are actually
A. the same.
B. rates but for different quantities.
C. the same when direction is not a factor.
D. the same when an object is freely falling.
Acceleration and velocity are actually
A. the same.
B. rates but for different quantities.
C. the same when direction is not a factor.
D. the same when an object is freely falling.
Explanation:
• Velocity is the rate at which distance changes
over time,
• Acceleration is the rate at which velocity
changes over time.
A free-falling object has a speed of 30 m/s at one
instant. Exactly 1 s later its speed will be
A. the same.
B. 35 m/s.
C. more than 35 m/s.
D. 60 m/s.
A free-falling object has a speed of 30 m/s at one
instant. Exactly 1 s later its speed will be
A. the same.
B. 35 m/s.
C. more than 35 m/s.
D. 60 m/s.
Explanation:
One second later its speed will be 40 m/s,
which is more than 35 m/s.
When Sanjay pushes a refrigerator across a
kitchen floor at a constant speed, the force of
friction between the refrigerator and the floor is
A.
B.
C.
D.
less than Sanjay’s push.
equal to Sanjay’s push.
equal and opposite to Sanjay’s push.
more than Sanjay’s push.
When Sanjay pushes a refrigerator across a kitchen
floor at a constant speed, the force of friction
between the refrigerator and the floor is
A. less than Sanjay’s push.
B. equal to Sanjay’s push.
C. equal and opposite to Sanjay’s push.
D. more than Sanjay’s push.
When Sanjay pushes a refrigerator across a kitchen
floor at an increasing speed, the amount of friction
between the refrigerator and the floor is
A. less than Sanjay’s push.
B. equal to Sanjay’s push.
C. equal and opposite to Sanjay’s push.
D. more than Sanjay’s push.
When Sanjay pushes a refrigerator across a kitchen
floor at an increasing speed, the amount of friction
between the refrigerator and the floor is
A.
less than Sanjay’s push.
B.
equal to Sanjay’s push.
C.
equal and opposite to Sanjay’s push.
D.
more than Sanjay’s push.
Explanation:
The increasing speed indicates a net force greater
than zero. The refrigerator is not in equilibrium.
Consider a cart pushed along a track with a
certain force. If the force remains the same
while the mass of the cart decreases to half,
the acceleration of the cart
A. remains relatively the same.
B. halves.
C. doubles.
D. changes unpredictably.
Consider a cart pushed along a track with a certain force.
If the force remains the same while the mass of the cart
decreases to half, the acceleration of the cart
A. remains relatively the same.
B. halves.
C. doubles.
D. changes unpredictably.
Explanation:
Acceleration = net force / mass
Because, mass is in the denominator,
acceleration increases as mass decreases.
So, if mass is halved, acceleration doubles.
At one instant, an object in free fall has a speed of
40 m/s. Its speed 1 second later is
A. also 40 m/s.
B. 45 m/s.
C. 50 m/s.
D. None of the above.
At one instant, an object in free-fall has a speed of
40 m/s. Its speed 1 second later is
A. also 40 m/s.
B. 45 m/s.
C. 50 m/s.
D. None of the above.
Explanation:
Anything in free fall increases the falling speed
by about 10 meters/second every second.
A 5-kg iron ball and a 10-kg iron ball are dropped
from rest. For negligible air resistance, the
acceleration of the heavier ball will be
A. less.
B. the same.
C. more.
D. undetermined.
A 5-kg iron ball and a 10-kg iron ball are dropped
from rest. For negligible air resistance, the
acceleration of the heavier ball will be
A. less.
B. the same.
C. more.
D. undetermined.
If a 50-N person is to fall at terminal velocity, the
air resistance needed is
A. less than 50 N.
B. 50 N.
C. more than 50 N.
D. None of the above.
If a 50-N person is to fall at terminal velocity, the
air resistance needed is
A. less than 50 N.
B. 50 N.
C. more than 50 N.
D. None of the above.
Explanation:
Then, F = 0 and acceleration = 0.
As a skydiver falls faster and faster through the air,
air resistance
A. increases.
B. decreases.
C. remains the same.
D. Not enough information.
As a skydiver falls faster and faster through the air,
air resistance
A. increases.
B. decreases.
C. remains the same.
D. Not enough information.
As a skydiver fall faster and faster through the air,
net force
A. increases.
B. decreases.
C. remains the same.
D. Not enough information.
As a skydiver fall faster and faster through the air,
net force
A.
increases.
B.
decreases.
C.
remains the same.
D.
Not enough information.
Explanation: The net force is the combined force on
the skydiver. As the air resistance builds up, it
cancels out more and more of the gravitational
force, which results in a smaller net force.
As a skydiver fall faster and faster through the air,
her acceleration
A. increases.
B. decreases.
C. remains the same.
D. Not enough information.
As the skydiver faster and faster through the air,
her acceleration
A. increases.
B. decreases.
C. remains the same.
D. Not enough information.
Explanation
If the net force decreases, so much the
acceleration according to F=ma.
(Newton’s 2nd Law)
When the air in a tube containing a coin and a
feather is removed,
A.
the feather hits the bottom first, before the coin hits.
B.
the coin hits the bottom first, before the feather hits.
C.
both the coin and feather drop together side-by-side.
D.
Not enough information.
When the air in a tube containing a coin and a
feather is removed,
A.
the feather hits the bottom first, before the coin
hits.
B.
the coin hits the bottom first, before the feather
hits.
C.
both the coin and feather drop together sideby-side.
D.
Not enough information.
Explanation: With no air resistance, they are in free fall
and accelerate at the same rate: g or 9.8 m/s2
Work is done in lifting a barbell. How much work is
done in lifting a barbell that is twice as heavy the
same distance?
A. Twice as much
B. Half as much
C. The same
D. Depends on the speed of the lift
Work is done in lifting a barbell. How much work is
done in lifting a barbell that is twice as heavy the
same distance?
A.
Twice as much
B. Half as much
C. The same
D. Depends on the speed of the lift
Explanation:
This is in accord with work  force  distance. Twice the
force for the same distance means twice the work done
on the barbell.
You do work when pushing a cart with a constant
force. If you push the cart twice as far, then the
work you do is
A. less than twice as much.
B. twice as much.
C. more than twice as much.
D. zero.
You do work when pushing a cart with a constant
force. If you push the cart twice as far, then the
work you do is
A. less than twice as much.
B. twice as much.
C. more than twice as much.
D. zero.
A job can be done slowly or quickly. Both may
require the same amount of work, but different
amounts of
A. energy.
B. momentum.
C. power.
D. impulse.
A job can be done slowly or quickly. Both may
require the same amount of work, but different
amounts of
A. energy.
B. momentum.
C. power.
D. impulse.
Comment:
Power is the rate at which work is done.
The work done in bringing a moving car to a stop is
the force of tire friction  stopping distance. If the
initial speed of the car is doubled, the stopping
distance is
A. actually less.
B. about the same.
C. twice.
D. None of the above.
The work done in bringing a moving car to a stop is
the force of tire friction  stopping distance. If the
initial speed of the car is doubled, the stopping
distance is
A.
actually less.
B.
about the same.
C.
twice.
D. None of the above.
Explanation:
Twice the speed means four times the kinetic
energy and four times the stopping distance.
A certain machine is 30% efficient. This means
the machine will convert
A. 30% of the energy input to useful work—70%
of the energy input will be wasted.
B. 70% of the energy input to useful work—30%
of the energy input will be wasted.
C. Both of the above.
D. None of the above.
A certain machine is 30% efficient. This means
the machine will convert
A. 30% of the energy input to useful work—
70% of the energy input will be wasted.
B. 70% of the energy input to useful work—30%
of the energy input will be wasted.
C. Both of the above.
D. None of the above.
A 1-meter-long pendulum has a bob with a
mass of 1 kg. Suppose that the bob is now
replaced with a different bob of mass 2 kg,
how will the period of the pendulum
change?
A. It will double.
B. It will halve.
C. It will remain the same.
D. There is not enough
information.
A 1-meter-long pendulum has a bob with a mass of
1 kg. Suppose that the bob is now replaced with a
different bob of mass 2 kg, how will the period of
the pendulum change?
A. It will double.
B. It will halve.
C. It will remain the
same.
D. There is not enough
information.
Explanation:
The period of a pendulum depends only on the
length of the pendulum, not on the mass. So
changing the mass will not change the period of
the pendulum.
If the frequency of a particular wave is 20
Hz, its period is
A.
1/
20
second.
B. 20 seconds.
C. more than 20 seconds.
D. None of the above.
If the frequency of a particular wave is 20 Hz,
its period is
A.
1/
20
second.
B. 20 seconds.
C. more than 20 seconds.
D. None of the above.
Explanation:
Note when  = 20 Hz, T = 1/ = 1/(20 Hz) =
1/
20 second.
The vibrations along a transverse wave move in a
direction
A. along the wave.
B. perpendicular to the wave.
C. Both A and B.
D. Neither A nor B.
The vibrations along a transverse wave move in a
direction
A. along the wave.
B. perpendicular to the wave.
C. Both A and B.
D. Neither A nor B.
Comment:
The vibrations in a longitudinal wave, in
contrast, are along (or parallel to) the direction
of wave travel.
The Doppler effect occurs for
A. sound.
B. light.
C. Both A and B.
D. Neither A nor B.
The Doppler effect occurs for
A. sound.
B. light.
C. Both A and B.
D. Neither A nor B.
Explanation:
The Doppler effect occurs for both sound and
light. Astronomers measure the spin rates of
stars by the Doppler effect.
Interference is a property of
A. sound.
B. light.
C. Both A and B.
D. Neither A nor B.
Interference is a property of
A. sound.
B. light.
C. Both A and B.
D. Neither A nor B.
.