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course PHY 2011
05/20/12 2:00
Samantha RogersPHY 201
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Question: `q001. There are two parts to this problem. Reason them out using common sense.
If the speed of an automobile changes by 2 mph every second, then how long will it take the speedometer to move from the 20 mph mark to the 30 mph mark?
Given the same rate of change of speed, if the speedometer initially reads 10 mph, what will it read 7 seconds later?
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Your solution:
30-20=10 total of 10 mph difference.
10mph/2mph = 5. It would take a total of 5 seconds if the speed was changing by 2 mph every second to get the speedometer to change from 20 mph to 30 mph.
Changing at the rate of 2 mph every second, in 7 seconds, the speedometer will change a total of 14 mph. If the speedometer initially read 10 mph then 10 + 14 = 24 mph.
confidence rating #$&*: 3
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Given Solution:
`aIt will take 5 seconds to complete the change. 30 mph - 20 mph = 10 mph change at 2 mph per second (i.e., 2 mph every second) implies 5 seconds to go from 20 mph to 30 mph
Change in speed is 2 mph/second * 7 seconds = 14 mph Add this to the initial 10 mph and the speedometer now reads 24 mph.
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Self-critique (if necessary): OK
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Self-critique Rating: 3