12A
Also, remember that the take home exam is due tomorrow.
Assignment 41 Energy
Basics and Conversion Practice Questions
Answer
all of the following questions to the best of your ability. SHOW YOUR WORK. You
are going to need looseleaf. Please do not try to be that kid that scrunches
their lame answer in between questions and does not show work. Please and thank
you.
1.
A 100 Watt incandescent light bulb uses 100 J/sec of electrical energy. If it
is 20% efficient, then the bulb converts 20% of the electrical energy into
light and 80% is wasted by being transformed into heat (light bulbs are hot).
a.
How does this demonstrate the 1st and/or 2nd Law of
Thermodynamics?
b. How much
energy (in joules) does the light bulb consume in a week?
c. Express
your answer to 1b. in kilowatt-hours (kWh).
2. Wes
wants to help his mom save money by not vacuuming the house daily. He suggests
that the house only needs to be vacuumed once a month. If their vacuum cleaner uses
1500 watts and it takes one hour to vacuum the house, how much can Wes save a
year if his mom accepts his plan? Assume 1 kWh costs $0.10.
3. The
average household consumes 10,000 kilowatt hours (kWh) a year. A family decides to add a solar water heater
to reduce their electric bill. The solar water heater will reduce their power
consumption by 20% each year. Assume 1 kWh costs $0.10, how much will they save
in five years?
4. The Cobb family of Fremont is looking at ways to decrease their
home water and energy usage. Their current electric hot-water heater raises the
water temperature to 140° F, which requires 0.20 kWh/gallon at a cost
of $0.10/kWh. Each person in the family of four showers once a day for an
average of 10 minutes per shower. The shower has a flow rate of 5.0 gallons per
minute.
a. Calculate the total amount of water that the family uses per
year for taking showers.
b. Calculate the annual
cost of the electricity for the family showers, assuming that 2.5 gallons per
minute of the water used is from the hot-water heater.
c.
The family is considering replacing their current hot-water heater with a new
energy-efficient hot-water heater that costs $1,000 and uses half the energy
that their current hot-water heater uses. How many days would it take for the
new hot-water heater to recover the $1,000 initial cost?
5. How does
today’s discussion of energy relate to sustainability?
12D
Assignment 41 Energy
Basics and Conversion Practice Questions
Answer
all of the following questions to the best of your ability. SHOW YOUR WORK and
write in complete sentences. You are going to need looseleaf. Please do not try
to be that kid that scrunches their lame answer in between questions and does
not show work. Please and thank you.
1.
A 100 Watt incandescent light bulb uses 100 J/sec of electrical energy. If it
is 20% efficient, then the bulb converts 20% of the electrical energy into
light and 80% is wasted by being transformed into heat (light bulbs are hot).
a.
How does this demonstrate the 1st and/or 2nd Law of
Thermodynamics?
b. How much
energy (in joules) does the light bulb consume in a week?
c. Express
your answer to 1b. in kilowatt-hours (kWh).
2. Wes
wants to help his mom save money by not vacuuming the house daily. He suggests
that the house only needs to be vacuumed once a month. If their vacuum cleaner
uses 1500 watts and it takes one hour to vacuum the house, how much can Wes
save a year if his mom accepts his plan? Assume 1 kWh costs $0.10.
3. The
environmental impact of washing a load of dirty dishes in an electric
dishwasher differs from that of washing them by hand in a sink. Use the
information and data below to answer the questions that follow. Show your
calculations.
Assume the
following:
·
The
dishes all fit in one load.
·
The
water coming into the water heater for the sink and into the water heater in
the dishwasher is at 50°F.
·
The
water heaters for the sink and the dishwasher are both 100 percent efficient.
·
In
one complete cycle, the electric dishwasher uses 10 gallons of water heated to
140°F and the dishwasher also uses 0.500 kilowatt-hour of electrical energy for
its mechanical operation.
·
Washing
the dishes by hand requires 20 gallons of water heated to 110°F.
Other
Information:
1 gallon of
water = 8 pounds of water
1 BTU = the
amount of energy needed to raise the temperature of 1 pound of water by 1°F
1
kilowatt-hour = 3,400 BTU
a.
Calculate the total energy (in BTU’s) used to heat the water and run the
electric dishwasher to wash a load of dishes.
b.
Calculate the energy (in BTU’s) used to heat the water for washing the load of
dishes by hand.
c. Discuss
the economic and environmental costs and benefits of
1. using the electric dishwasher
(including its manufacture and disposal)
2. washing the dishes by hand
4. Answer the questions below
regarding the heating of a house in Minnesota. Assume the following.
• The house
has 2,000 square feet of living space.
• 80,000
BTUs of heat per square foot are required to heat the house for the winter.
• Natural
gas is available at a cost of $5.00 per thousand cubic feet.
• One cubic
foot of natural gas supplies 1,000 BTUs of heat energy.
• The
furnace in the house is 80 percent efficient.
Calculate
the following, showing all the steps of your calculations, including units.
a. The
number of cubic feet of natural gas required to heat the house for one winter
b. The cost
of heating the house for one winter
5. How does
today’s discussion of energy relate to sustainability?
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