AP 07 Enviornmental Sci
AP® ENVIRONMENTAL SCIENCE
2007 SCORING GUIDELINES
Question 2
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 following. Be sure to show all your work and include units with your
answers.
(i) The total amount of water that the family uses per year for taking showers (2 points—
1 point for correct set-up and 1 point for correct answer with units)
10 minutes/day x 5 gallons/minute x 365 days/year x 4 (people) = 73,000 gallons/year
(73,000 gallons also acceptable due to usage defined as per year)
(ii) 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 (2 points—1 point for correct setup and 1 point for correct answer with units)
73,000 gallons/year ÷ 2 = 36,500 gallons of hot water per year
36,500 gallons/year x 0.20 kWh/gallon x $0.10/kWh = $730/year
($730 also acceptable due to cost defined as per annum)
(b) The family is considering replacing their current hot-water heater with a new energyefficient hot-water heater that costs $1,000 and uses half the energy that their current hotwater heater uses. How many days would it take for the new hot-water heater to recover
the $1,000 initial cost? (2 points—1 point for correct set-up and 1 point for correct answer
with units)
Old bill for electricity = $730/year = $2/day
($730/yr ÷ 365day/year = $2/day)
New bill for electricity = $730 ÷ 2 = $365/year
$365/yr ÷ 365 day/year = $1/day = new cost per day
Old cost = $2/day, new cost = $1/day
Savings old – new = $1/day
Days to pay off initial cost = cost ÷ $saved/day = $1,000 ÷ $1/day = 1,000 days
(1,000 also acceptable due to days stated in the question)
With the old heater they were spending $2/day for hot water for showers; with the new heater they
would spend $1/day for hot water for showers. Therefore, the savings is $1/day, and they would
recover the $1,000 cost of the new hot-water heater in 1,000 days.
Savings calculation alone:
0.2kWh/gallon ÷ 2 = 0.10kWh/gallon saved
0.10kWh/gallon x 2.5 gallons/minute x 10 minutes/person x 4 people x $0.10/kWh = $1/day
$1,000 ÷ $1/day = 1,000 days
Another way of looking at it:
The new hot-water heater would mean a savings of $365 per year. $1,000 ÷ $365/year = 2.74 years
2.74 years x 365 days/year ≈ 1,000 days (1,000 also acceptable due to days given in problem)
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AP® ENVIRONMENTAL SCIENCE
2007 SCORING GUIDELINES
Question 2 (continued)
(c) Describe TWO practical measures that the family could take that would reduce their
overall water use at home. (2 points total—1 point for each measure)
Valid answers to this question include:
Reduce the length of daily showers
Shower less frequently
Install low-flow shower heads and/or toilets
Make sure all water leaks are fixed
Don’t let water run while brushing teeth
Run the dishwasher or washing machine only when fully loaded
Use a water-efficient appliance
Hand washing dishes uses less water then running a dishwasher
Use of paper plates and plastic silverware; not using the dishwasher
Use plants outside that require little watering/only water on alternate days/use drip irrigation
systems/moisture sensing sprinklers
Sweeping driveway/sidewalks versus washing with water
Don’t let water run while washing the car
Wash the car less frequently
Use a car wash
Reuse of water—gray water, bucket in shower to later water plants, rain barrel, etc.
(d) Describe TWO conservation measures (other than reducing hot water use) that the family
could take to reduce the total amount of energy that they use at home. (2 points—1 point
for each measure)
Valid answers to this question include:
Turn off electric appliances when no one is in the room
Turn off lights in daylight hours
Replace incandescent light bulbs with fluorescents
Increase insulation
Set thermostat to higher temperatures in the summer and lower temperatures in the winter
Use an automatic thermostat that lowers/raises temperatures when no one is in the house
Replace appliances with energy-efficient appliances
Caulk and/or weather-strip exterior doors and windows
Replace single-pane windows with double-pane or other more energy-efficient windows
Open windows/run fans rather than running air-conditioning
Use sweaters/blankets rather than running heater
Reduce usage by not using appliances—hand wash vs. dishwasher
Unplug appliances when not in use.
Line dry clothing instead of using dryer
Lower thermostat of water heater
Add insulation blanket to the hot water heater
Purchase more energy-efficient water heater
Use of passive solar with description
© 2007 The College Board. All rights reserved.
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©2007 The College Board. All rights reserved.
Visit apcentral.collegeboard.com (for AP professionals) and www.collegeboard.com/apstudents (for students and parents).
©2007 The College Board. All rights reserved.
Visit apcentral.collegeboard.com (for AP professionals) and www.collegeboard.com/apstudents (for students and parents).
©2007 The College Board. All rights reserved.
Visit apcentral.collegeboard.com (for AP professionals) and www.collegeboard.com/apstudents (for students and parents).
©2007 The College Board. All rights reserved.
Visit apcentral.collegeboard.com (for AP professionals) and www.collegeboard.com/apstudents (for students and parents).
©2007 The College Board. All rights reserved.
Visit apcentral.collegeboard.com (for AP professionals) and www.collegeboard.com/apstudents (for students and parents).
AP® ENVIRONMENTAL SCIENCE
2007 SCORING COMMENTARY
Question 2
Overview
The purpose of this data-based question was to assess the students’ ability to analyze information, to
calculate water use and electricity costs, and to calculate the cost savings from replacing an old water
heater with a more efficient one. It also measured students’ ability to recognize home water conservation
and energy conservation measures.
Sample: 2A
Score: 10
Part (a): Two points were earned in (a)(i): 1 point for correctly calculating the number of gallons used per
year for showering, and 1 point for the correct answer with units. Two points were earned in (a)(ii): 1 point
for correctly calculating the annual cost in dollars per year for electricity in the setup, and 1 point for the
correct answer with units.
Part (b): Two points were earned: 1 point for correctly calculating the savings per year from the new hotwater heater in the setup, and 1 point for the correct answer.
Part (c): Two points were earned for water conservation measures: 1 point for “shorter showers” (reducing
the length), and 1 point for turning “off the sprinklers when it is raining outside.”
Part (d): Two points were earned for energy conservation measures: 1 point for turning “off unused lights,”
and 1 point for turning “off the computer when it’s not being used.”
Sample: 2B
Score: 6
Part (a): Two points were earned in (a)(i): 1 point for correctly calculating the number of gallons used per
year for showering, and 1 point for the correct answer with units. No points were earned in (a)(ii). The
student incorrectly calculates the annual cost in dollars per year for electricity in the setup, and no point
was earned for an incorrect answer.
Part (b): No points were earned. The student incorrectly calculates the savings per year from the new hotwater heater in the setup by neglecting to account for the four people in the family. No point was earned
for an incorrect answer.
Part (c): Two points were earned for water conservation measures: 1 point for watering “the lawn less” and
“at night” to reduce evaporation losses, and 1 point for purchasing “a low-flush [flow] toilet.”
Part (d): Two points were earned for energy conservation measures: 1 point for better insulation, and
1 point for using more energy-efficient fluorescent lights rather than incandescent lights.
Sample: 2C
Score: 3
Part (a): No points were earned in (a)(i). The student incorrectly calculates the number of gallons used per
year for showering, and no point was earned for the incorrect answer. No points were earned in (a)(ii). The
student incorrectly calculates the annual cost in dollars per year for electricity in the setup, and no point
was earned for an incorrect answer.
© 2007 The College Board. All rights reserved.
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AP® ENVIRONMENTAL SCIENCE
2007 SCORING COMMENTARY
Question 2 (continued)
Part (b): No points were earned. The student does not show a setup, and no point was earned for an
incorrect answer.
Part (c): Two points were earned for water conservation measures: 1 point for reducing “the amount of time
they take showers,” and 1 point for taking “a shower every other day.”
Part (d): One point was earned for energy conservation measures (for not using electronic appliances). The
cooler showers did not earn a point, because the question states that conservation measures must be other
than from reducing hot water use. The remainder is an insufficient description involving energy
conservation.
© 2007 The College Board. All rights reserved.
Visit apcentral.collegeboard.com (for AP professionals) and www.collegeboard.com/apstudents (for students and parents).
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