Answer to Question 1
The air conditioners have a cooling capacity measured in Btu in the United States.
To achieve a given level of cooling requires so many Btus. The cooling efficiency rating
means the cost in Wh needed to achieve the desired Btu level. In order to make this
calculation, we need to assume something about how many degree days of cooling are
needed. This varies widely. The more the unit is used, the more savings accumulate for the
more efficient unit. Then we have to figure the correlation of Btus needed to reduce the
temperature to the desired temperature. We can answer the question by comparing the two
without all these assumptions, however.
Consider the more efficient air conditioner. It produces an effect of 16.4 Btu/Wh, which is
almost twice the efficiency of the average unit (actually, 1.89 times as efficient). This means
that, for a given amount of cooling, it will cost only 0.53 as much with the efficient air
conditioner as with the average air conditioner. Or, conversely, it will cost 1.89 times as
much with the less efficient average air conditioner. If we assume a summer's use of 4000
kWh for air conditioning for the less efficient air conditioner, probably not a bad
assumption, we would pay 320 for cooling. The cost would be only 169.76 with the
more efficient air conditioner. Over 14 yr, the energy cost would be 2377 instead of
4480, for a savings of 2103 . If the use were less than 4000 kWh or more, the savings
would dip or rise accordingly.
Answer to Question 2
The car's velocity has changed all along its path. Coming downhill, the car
speeded up. Going uphill, the car slowed down. At the bottom of the hill, the velocity
changed direction.
Without more information about the steepness of the hills, it is impossible to judge where
the change was greatest. We know we need to know how steep to know how fast the car's
velocity was changing from our experience. A car on a flat surface will not begin to roll. A
gentle incline can start the car rolling slowly. A steep incline can make the car roll quickly.
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