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W __ 0The environment does work on the system and the system’s
energy increases.
W __ 0The system does work on the environment and the system’s
energy decreases.
Energy transformations
within the system ______
change the value of E
sys
.
Systems are typically not
___________ from their
environment and therefore
exchange energy with the
environment.
The
mechanical transfer of
energy is called ________.
Work
 Chapter 11
Positive, Negative and Zero Work
Keep track of whether work is positive, negative, or zero.
Positive work _____________ speed.
Negative work _____________ speed.
Zero work has _____________ on speed.
Apple Falls
W __ 0
Apple ______
W ____ 0
Apple __________
∆
r
∆
r
mg
mg
Work
dt
dv
m
ma
F
s
s
s
=
=
ds
dv
mv
dt
ds
ds
dv
m
dt
dv
m
s
s
s
s
=
=
ds
dv
mv
F
s
s
s
=
s
s
s
dv
mv
ds
F
=
∫
∫
=
f
i
f
i
v
v
s
s
s
s
s
dv
mv
ds
F
2
i
2
f
v
v
2
s
s
s
s
mv
2
1
mv
2
1
mv
2
1
ds
F
f
i
f
i
−
=
=
∫
___________
Work
2
i
2
f
v
v
2
s
s
s
s
mv
2
1
mv
2
1
mv
2
1
ds
F
f
i
f
i
−
=
=
∫
You will also notice that this equation also reads that ___________.
To change a particles energy, a ___________ must be applied to the
particle as it undergoes
a displacement.
v
i
v
f
Σ
F
∆
x
K
mv
2
1
mv
2
1
ds
F
W
2
i
2
f
s
s
s
f
i
∆
=
−
=
=
∫
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In the simplest case, when
the force
F
and the
displacement
∆
r are
____________
, this
definition of the work is
given by
W = F
∆
r
[W] = ______ = J = joule (J)
named for James Prescott Joule
In general, work is the component of the the force parallel
to the
displacement multiplied by the displacement.
So, only forces in
the direction of _______________ count.
∆
r
F
___________
Work
W = F
∆
r _______
F = 50.0N
∆
r = 10.0m
θ
= 30.0
0
W = 50.0N (10.0m) ____________
= 430 Nm = 430 J
Example: Hannah’s grandma
pulls a wagon with a force of 50.0
N.
The handle makes a 30.0
o
angle with the ground.
The
wagon moves 10.0m.
Calculate
the work.
Note: the ___________ force does no work since it is
_________________ to the displacement
Work is the component
of the the force parallel
to the displacement
multiplied by the
displacement.
Accelerate the Car
To accelerate a car from rest to a speed v requires the work W
1
.
The work needed to accelerate the car from v to 2v is W
2
.
Using the work – energy theorem: W
net
= _________________
Let’s calculate W
1
v
i
= ___, v
f
= _____
W
1
= ______________________________
Calculating W
2
v
i
= _____, v
f
= ________
W
2
= _____________________
W
2
= ____W
1
Kinetic Energy
a) K
f
= ___________
K
f
= W
net
+ _____
K
f
= ____________ = 4500 N (100 m)
= 4.5 x 10
5
J
b) _________ = F
∆
x = 4.5 x 10
5
J
v = 25.4 m/s
m
J
x
v
)
10
5
.
4
(
2
5
=
A 1400 kg boat has a forward force of 4500 N applied.
The boat starts from rest and travels 100 m.
What is
the final kinetic energy and the velocity of the boat?
Friction does _____ work on the car.
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This note was uploaded on 04/17/2008 for the course PHYSICS 122 taught by Professor Pope during the Spring '08 term at Clemson.
 Spring '08
 pope
 Energy, Work

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