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Unformatted text preview: We developed he model that work done by a force outside of a system (Fm) will change one or more of the
energies within the system. If the system contains the object of interest, the system can have kinetic energy.
If it also contains the earth, then it can have both gravitational potential energy and kinetic energy.
So far, those are the only energies we ’1] consider. There are more, and we ’11 get to them soon enough. For each of the following situations:
Identify a system, the initial and ﬁnal states.
List external forces doing work on the system. Describe energy transformation processes using energy bar charts
21' x O
i .1». ‘ Lifting a block up with the acceleration ?(exactly as was discussed in lecture) «warm—em 6* L’IW'R‘ . ~ ___..—.——/l\ h2
“ ' (MUM, 4 W
1
v Rope ——9 g Ian/AL —’> ML (“new (Nisaeneas)
’ ' .0 1720?; his ! H
—————————— ,————— ——————  Earth' 3 D + = _~
A “l K" l W K
2. Lifting a block up an inclined plane a distance 1 along the plane with constant
speed. i.
a 21“
5mm l EMZM . 'Sys'n‘adq
tawny, __, h: LBOWM at PIAis)
9”” 4‘11. (to! or ﬂow?) MOTOR W at
N WORKSHOP. HVTRODUCHON TO WORK AND ENERGY A' ‘1
‘3’???
x3???
I. Workshop Skills: Energy Transformations ., ' ‘33: II. Invneting an Index
A..The car washing inefﬁciency index You're the managerxof a chain of area car washes in which teams of employees wash the
cars by hand. It's time for your annual review of team performance, so you take data — about how long it takes each of the teams to wash different cars. You want to ﬁnd out
which team is the most inefﬁcient so it can be retrained. The teams don't all have the same number of people, however, so how can you determine which team is the most inefﬁcient?
REMEMBER: THE BIGGER INDEX MEANS THAT THE TEAM IS MORE ' INEEFFICIENT Invent a procedure for computing a car washing inefﬁciency index for each team. Wash Time: 6.8 minutes I I ' $.Wash Time: 10.5 minutes Wash Time: 8.4 minutes M097”
(NETHUWT B. The weightlifting index Several of your friends have been bragging about how strong they are. To settle the
matter, they have decided to hold a weightlifting contest, and you've been recruited as a
judge because there's nothing a physicist knows more about than feats of physical
strength. The problem is they don‘t agree on how to score the competition, since they all
lift different amounts of weight and they liﬁ the weights to diﬂ‘erent heights. Invent a procedure for computing a weightlifting index for each competitor.
REMEMBER: THE BIGGER INDEX MEANS STRONGER / . JAEK ‘DIESEL 7 "ﬂ C. Job Difﬁculty index 
Some friends are complaining about their summer jobs. Each person thinks he works the
hardest out of everyone. All their jobs are different, so it's difﬁcult to tell. You've been
asked to decide once and for all whose job is the most difficult. Invent a 'ob difﬁcul index for the workers and rank them from hardest to easiest ’ob. Name 1 Job Force Distance Force ‘ Distance
W exerted. exerted Lifts 1ce blocks in a meat packing plant Pushes a luggage cart at the airport 400 N 124 N 1
Monty Carries old computers up a ladder to an attic 200 N 72 m 240 N storae facili
Rolls oil drurgs up a ramp to a truck bed 230 N , 345 N Reasoning Questions:
.9Discuss in everyday language what the numeric value of the car washing inefﬁciency index tells you about each team. (Hint: Think about what the
number means if the team has only 1 person, or, alternatively, what would it
take to wash a car in 1 minute?) N o \l
I!
..i DJ 00 I v ‘ 2. Which car washing team is the most inefﬁcient? 3. Assuming their index is a constant, how long would it take Shimmy Shine to
wash the truck if one of their members brought in two of his friends to help? 4. How many people would Klean Whips need to wash a sports car in 4 minutes? Discuss in everyday language what the numeric value of the weightlifting index
" tells you about each competitor. 5" Which competitor won the competition? IfBatman had attempted to lift 150 kilograms, how far would he have lifted it?
What mass could Mikhail McMuscles lift to 1.25 meters? 99°F)? The competitors are thinking of trying out for the cheerleading team.
Applicants must be able to lift 90 POUNDS to a height of 2 meters. Which
applicants should go to the tryouts and which should look for other activities? 10. How do you know which summer job is the most difﬁcult? Explain in everyday
language how you decided whose was the most difﬁcult job. 11. At Burley’s meat—packing plant they decided to double the width of the ice
blocks, making them twice as heavy. Assuming Burley’s job difﬁculty index
doesn’t change, what else will change about his job? How will it change? 12. Discuss in everyday language what the numeric value of job dzﬂiculgz index
tells you about the job. ...
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This note was uploaded on 02/06/2012 for the course PHYSICS 115 taught by Professor Brahmia during the Fall '08 term at Rutgers.
 Fall '08
 Brahmia
 Physics, Energy, Work

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