In 2000, you have a choice between keeping your 13-year-old model that uses 515 kWh/yr or buying one that uses 440 kWh/yr
Given the average refrigerator lifetime of 19 years, would you save money or spend money overall by 2006 if you bought the efficient model for $500? Suppose you know that the best refrigerator available in 2006 when the old one really bites the dust will use 380 kWh/yr. Should that affect your decision to buy now? Explain.
We use the same method as in question 36 . The total cost of the more efficient
refrigerator will be
$500.00 + N x 440 kWh/yr x $0.10/kWh
= $500.00 + N x $44.00/yr = $764.00,
where N is the number of years the refrigerator is used (6 here). Because we scrapped the
old refrigerator (presumably, it had lasted its 19 yr lifetime), its cost is irrelevant (and it
possibly couldn't have been used).
The cost of the old model you own over those 6 years is
(6 years) x (515 kWh/yr) x $0.10/kWh = $309.00
So, you would have spent a net of $455.00 more for the more efficient model.
The next 13 years life remaining of the more efficient refrigerator over the following 13
years would cost
(13 years) x $44.00/yr = $572.00
Meanwhile, if you'd bought the 380 kWh/yr model in 2006, you'd pay
$500 + (13 years) x $38.00/yr = $994.00
over the rest of the lifetime of the 440 kWh model.
To answer the last question, add the $309.00 for letting the older refrigerator live out its
lifetime to the $994.00 for 13 years of the 380 kWh model to see the total cost over the 19-
year lifetime of the 440 kWh model, that is, $1013.00 total cost. Buying the 440 kWh
model and running it for its 19-year lifetime would have cost $500.00 + (19 years) x
$44.00/yr = $1336.00 . If you knew the energy use would decline as much as this, it is in
your economic interest to wait until the old refrigerator gives up the ghost.
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During the time that a planet is in its period of apparent retrograde motion
A) The planet moves backwards (clockwise as viewed from above Earth's north pole) in its orbit of the Sun. B) The planet appears to rise in the west and set in the east, rather than the usual rising in the east and setting in the west. C) Over many days or weeks, the planet moves westward relative to the stars, rather than the usual eastward relative to the stars. D) The planet is getting closer to the Sun in its orbit.
This multiple exposure photograph shows the apparent retrograde motion of Mars. To make this picture, the photographer needed to combine individual photos of Mars taken over a period of
A) one full night. B) about one hour. C) about 3 nights. D) several months.
Which of the following atoms normally has one covalent bond to it?
a. I b. O c. C d. P e. Kr
If kerosene costs 130. Passi per liter, and one dollar buys 227. Passi; what is its cost in DOLLARS per GALLON? [1.00 gallon = 3.79 liters]
What will be an ideal response?