Download Equation Sheet for Physics 103 Midterm 2 Efficiency = Useful

Equation Sheet for Physics 103 Midterm 2
W = F D
Efficiency = Useful Energy Out
Total Energy In
Efficiency
F =
Work out
Eff =
Work in
E
G M1 M 2
pot
D2
= M g h
F = Ma
E kin = _ M v 2
F = Mg
Actual Mechanical Advantage
s
=
D
t
Theoretical Mechanical Advantage
a = vf – vi
t
F
=
E cap
=
I =
k Q1 Q 2
Q
t
V = I R
D2
=
1
Q V final
2
P = E
t
= W
t
Q = C V
P = I V
E pot = Q V
R
G = 6.67 x 10 –11 N m2/kg2
=
ρ L
A
g = 9.8 m/s2 = 32 ft/s2
1 mile = 5,280 feet = 1.609 kilometers
1 foot = 0.305 meters
1 lb = 4.45 N
1 hour = 3600 seconds
1 joule = 0.74 foot pounds
1 horsepower = 746 watts
1 kilowatt = 1,000 watts
k = 8.99 x 10 9 N m2/coulomb2
92
F out
F in
=
Din
Dout
Second Midterm 2B
1.
Which of the following devices could be used to store electrical energy in the
form of electrical charge?
a)
b)
c)
d)
e)
2.
Which of the following statements is TRUE?
a)
b)
c)
d)
e)
3.
Protons move easily from one atom to the next.
Protons have a positive charge and neutrons have a negative charge.
Positive charges are attracted to one another, but negative charges are
repelled by one another.
Negative charges are attracted to one another, but positive charges are
repelled by one another.
Opposite charges are attracted to one another, but like charges are
repelled by one another.
Joe has a capacitor for which the capacitance rating has been rubbed off. In
-4
charging the capacitor, Joe finds that an average current of 4 x 10 amperes for
10 seconds will result in a voltage across the capacitor of 2 volts. What is the
capacitance of Joe's capacitor?
a)
b)
c)
d)
e)
4.
a capacitor
a battery
a water tank located above an electrically driven water pump
a fuse
All of the above devices could be used to store electrical energy in the
form of electrical charge.
-6
2 x 10 farads
-6
8 x 10 farads
-3
2 x 10 farads
-3
8 x 10 farads
20 farads
A toaster requires 120 volts and 1200 watts for proper operation. What is the
toaster's resistance when it is operating?
a)
b)
c)
d)
e)
0.01 ohms
1.2 ohms
12 ohms
120 ohms
240 ohms
100
5.
Why did the Leyden jar capacitor store more charge than the soda can
capacitor?
a)
b)
c)
d)
e)
6.
An Olympic athlete can generate about 735 watts of power. How much work can
she do in 1 minute?
a)
b)
c)
d)
e)
7.
735 joules
1,225 joules
4,410 joules
12,250 joules
44,100 joules
-3
In class, we discharged a large, 1 x 10 farad capacitor through a light bulb. If
the capacitor was charged to 250 volts, what was the charge on the capacitor?
a)
b)
c)
d)
e)
8.
The soda can is not a conductor.
The Leyden jar can store both positive and negative charge.
The Leyden jar had a wire connecting the two plates together.
The Leyden jar can store only one kind of charge.
All of the above are reasons why the Leyden jar can store more charge.
0.25 coulombs
0.125 coulombs
-4
2 x 10 coulombs
-6
2 x 10 coulombs
-6
4 x 10 coulombs
In class we had a tug-of-war with a winch. Suppose that you exerted a force of
200 newtons on the winch handle and moved it around in a circle a total
distance of 100 meters. The winch moved the rope a distance of 2 meters.
Neglecting friction, what was the force on the rope?
a)
b)
c)
50 newtons
200 newtons
4,000 newtons
d)
e)
10,000 newtons
40,000 newtons
101
9.
The cost of using a 1,200 watt hair dryer for 15 minutes every day for a year is
$8.76. What is the cost of electricity per kilowatt hour?
a)
b)
c)
d)
e)
10.
Simple machines make it easier to accomplish some tasks. Which of the following
statements about simple machines is TRUE
a)
b)
c)
d)
e)
11.
Simple machines can reduce the work required to move a load.
Because of friction, the energy input to a simple machine is usually less
than the energy transferred to the load.
A simple machine can provide a large output of force from a small input
of force.
For all simple machines, the distance the load is moved is always equal to
the distance through which the force is applied.
Simple machines are being replaced by automation all over the world.
A circuit consists of a 10 volt battery and two identical light bulbs in series.
Assuming no voltage drop occurs across any of the connecting wires in the
circuit, the voltage drop across the first light bulb is
a)
b)
c)
d)
e)
12.
$0.075
$0.08
$0.09
$0.105
$0.11
10 volts, the voltage boost provided by the battery.
less than 10 volts but more than 5 volts, because the current reaches this
bulb first.
5 volts, because each bulb uses the same amount of energy.
less than 5 volts, because it takes more energy to light the second bulb.
0 volts, because all of the voltage drop takes place across the second
bulb.
If the electric company charges $0.10 for each kilowatt-hour of electrical energy
used, how much will it cost you to use a 3000 watt oven for 1.5 hours each
month for one year?
a)
b)
c)
d)
e)
$0.45
$1.80
$3.60
$4.50
$5.40
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13.
Lisa and Bart are each required to lift 10 identical boxes from the floor and put
them on a table. Lisa does the job in exactly half the time that Bart took. Which
of the following statements about Lisa and Bart is TRUE?
a)
b)
c)
d)
e)
14.
In class your instructor used a block and tackle to lift two cement blocks. The
theoretical mechanical advantage of the block and tackle system was 6. Its
actual mechanical advantage was
a)
b)
c)
d)
e)
15.
less than 6 because there were two blocks.
less than 6 because of friction between the ropes and pulleys.
also 6 because theoretical and actual mechanical advantage are usually
equal.
greater than 6 because the instructor pulled down farther than the blocks
went up.
greater than 6 because of the inevitable waste of energy.
According to the video The Hidden City, which of the following is a major source
of power for New York City?
a)
b)
c)
d)
e)
16.
Lisa does half as much work as Bart, and in doing so produces an
average of half as much power as Bart.
Lisa does the same amount of work as Bart, and in doing so produces an
average of twice as much power as Bart.
Lisa does half as much work as Bart, and in doing so produces an
average of twice as much power as Bart.
Lisa does the same amount of work as Bart, and in doing so produces the
same average amount of power as Bart.
Lisa does twice as much work as Bart, and in doing so produces an
average of twice as much power as Bart.
dams along the Hudson River
hydroelectric power imported from Canada
tidal generating plants along New York's harbor
solar collectors on the Empire State Building
All of the above are major power sources for New York City.
A Quick Clean dishwasher costs $320 to purchase and uses 1,000 kWh for one
year of operation. A Scum Saver dishwasher costs $640 to purchase and uses
360 kWh for one year of operation. If electricity costs $0.10 per kWh, what is
the payback time for the Scum Saver dishwasher?
a)
b)
c)
d)
e)
0.36 years
2 years
2.8 years
5 years
64 years
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17.
The video Edison's Miracle of Light discussed the rise and fall of Edison's direct
current (DC) electric utility companies. Why did Edison's system of electrical
utilities not succeed?
a)
b)
c)
d)
e)
18.
Two identical capacitors were given identical charges. The first capacitor was
connected to an electric motor which ran for 10 seconds. The second capacitor
was connected to a flash bulb which lit up for one tenth of a second. Which of
the following statements is TRUE?
a)
b)
c)
d)
e)
19.
Edison's direct current utilities required costly transformers.
Edison's direct current utilities were only efficient when the generating
plant was far from the electric consumer's home or business.
Edison's direct current utilities could not transmit power efficiently over
long distances.
Edison's company was bought out by the natural gas industry.
Edison's carbon filament light bulbs did not last long enough to satisfy
consumers.
The energy stored in each capacitor was the same, but the power
produced by the capacitor connected to the flash bulb was greater.
The energy contained in the capacitor connected to the flash bulb was
greater, but the power produced by each capacitor was the same.
The energy contained in the capacitor connected to the flash bulb was
greater, and the power produced by that capacitor was greater.
The energy contained in the capacitor connected to the motor was
greater, and the power produced by that capacitor was greater.
The energy stored in each capacitor was the same, and the power
produced by each capacitor was the same.
When you plug in a toaster and turn it on, is there a complete circuit? Why?
a)
b)
c)
d)
e)
Yes. The electrical cord contains two wires to complete the circuit.
Yes. The toaster is "grounded" by resting on a countertop. This
completes the circuit from the wall.
No. You do not need to complete a circuit when you are operating with
alternating current (AC).
No. Complete circuits are only used in scientific experiments. They are
too expensive for general use.
Yes. The circuit is completed when the current from the wall is dissipated
in the air surrounding the toaster.
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20.
Jeff has connected together two simple machines in series, for a mechanical
advantage of 12. Jeff understands how the second machine works, and knows it
has a mechanical advantage of 4, but he does not understand the first machine,
and has not been told what its mechanical advantage is. Which of the following
statements is CORRECT?
a)
b)
c)
d)
e)
21.
Which of the following is most likely to increase the resistance of a resistor?
a)
b)
c)
d)
e)
22.
increasing its temperature
placing it in a strong magnetic field
putting a second resistor in parallel with it
decreasing its temperature
None of the above will affect the resistance of the resistor.
When the spinning disk of an electric meter mounted on the outside of a house
makes one full revolution, the amount of electrical energy that has been used
equals 0.60 watt-hours. How many joules of electrical energy have been used?
a)
b)
c)
d)
e)
23.
Jeff has no way of knowing the mechanical advantage of the first
machine.
The mechanical advantage of the first machine is 3.
The mechanical advantage of the first machine is 4.
The mechanical advantage of the first machine is 12.
The mechanical advantage of the first machine is 16.
0.6 joules
36 joules
2
8.6 x 10 joules
3
2.2 x 10 joules
3
3.6 x 10 joules
Sara can lift weights up to a maximum of 600 newtons. She has one machine
with a mechanical advantage of 2 and another with a mechanical advantage of
3. What is the maximum amount of weight she can lift by using the two
machines together as a complex machine?
a)
b)
c)
d)
e)
300 N
600 N
3000 N
3600 N
6000 N
105
24.
Sam uses a lever to raise a weight of 400 lbs. He applies a force of 80 lbs. to
the lever and the lever moves down at his end by a distance of 6 inches. Which
of the following statements is TRUE?
a)
b)
c)
d)
e)
25.
If electricity costs $0.08 per kilowatt hour (kWh), how many hours can one burn
a 100 watt light bulb for $16.00?
a)
b)
c)
d)
e)
26.
200 hours
1,500 hours
2,000 hours
5,000 hours
20,000 hours
A 12 volt car battery can supply a sustained 50 ampere current. If an electric car
needs 37,200 watts of power to operate properly, how many batteries are
needed to supply this power?
a)
b)
c)
d)
e)
27.
The work done by Sam 200 ft-lbs.
The work done by Sam is 160 ft-lbs.
The work done by Sam is 40 ft-lbs.
The gravitational potential energy increase of the weight is 400 ft-lbs.
None of the statements is true.
600 car batteries
62 car batteries
6 car batteries
1 car battery
0.1 car batteries
The amount of coal used by an electric power plant is given below:
Year
1992
1994
1996
Coal used
50,000 tons
100,000 tons
200,000 tons
If this pattern of growth of coal use continued, how much coal was used in
1998?
a)
b)
c)
d)
e)
300,000
350,000
400,000
600,000
750,000
tons
tons
tons
tons
tons
106
28.
The resistance of the human body is ordinarily about 20,000 ohms, but if a
person's hands are wet this resistance may be considerably reduced, perhaps to
as low as 5,000 ohms. What current would pass through a person's body who
was holding a hot wire connected to a 120 volt outlet in one wet hand and the
cold wire connected to the outlet in the other wet hand?
a)
b)
c)
d)
e)
29.
A person who can generate 200 watts of power while pedaling a bicycle
connected to a generator gets a part-time job generating electricity. If the
person is paid 10 cents per kilowatt-hour, how much money will the person
make per hour?
a)
b)
c)
d)
e)
30.
0.024 amperes
0.20 amperes
0.44 amperes
2.5 amperes
46 amperes
$20
$2
20 cents
2 cents
0.2 cents
You lift a box weighing 250 pounds, using a block and tackle. You pull
downward on the pulley rope with a force of 15 pounds. What is the mechanical
advantage of the block and tackle? Neglect friction.
a)
b)
c)
d)
e)
17
1.1
less than 100%
6%
The mechanical advantage can not be calculated because the distance
the box of books is lifted is not given.
107