In 2000, you have a choice between keeping your 13-year-old model ...

[altibaby]

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.

Question 2

Electric forces are
 
  a. the same as electric charges.
  b. exerted between all objects.
  c. exerted between any charged objects.
  d. exerted between pieces of tape only.
  e. not exerted except between manmade objects.

[bookworm410]

Answer to Question 1

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.

Answer to Question 2

B

[altibaby]

Thank you!

[bookworm410]

Always glad to help...