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Chapter 1011: Force, Work, Energy
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View Full Document Work & Kinetic Energy
Push a crate with a constant force as indicated.
v
A
=0
v
B
=?
F
A
B
dK
mv
d
mvdv
Fdx
=
=
=
)
(
2
2
1
A
B
B
A
B
A
K
K
mv
d
Fdx
−
=
=
∫
∫
)
(
2
2
1
Work=
Kinetic
Energy
=
Work & Potential Energy
F=Mg
m
y
B
=h
y
A
=0
Work: lift a crate from the ground
(y=0) to a height
h.
dU
mgy
d
mgdy
Fdy
=
=
=
)
(
A
B
y
y
y
y
U
U
Mgy
d
Fdy
B
A
B
A
−
=
=
∫
∫
)
(
Work=
Potential
Energy
=
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View Full Document Definition of Work
If the
force
and displacement are in
the same direction, work is defined
as:
ds
F
dW
⋅
=
ds
F
Work
B
A
∫
=
The work is done over a distance
by force F:
Displacement
Force
AB
Area
under
Force
=
ds
dW
Properties of Work
(1) Work can be used to change kinetic energy:
2
2
1
2
2
1
A
B
A
B
mv
mv
K
K
Work
−
=
−
=
(a) Push: increase kinetic energy
(b) Drag: decrease kinetic energy
(2) Work can be used to change potential energy:
(a) Gravitational energy: Work=U
B
U
A
=mg(y
B
y
A
)
(b) Elastic energy: Work=U
B
U
A
=
1/2
·k(
∆
x
B
)
2

1/2
·k(
x
A
)
2
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View Full Document Problem Solving 1
A 10kg bucket of water is lifted out of a well (5m
deep) by a man. The work done by the man is
about:
Force:
F=mg=10kg
×
10m/s
2
=100N
Displacement:
∆
y=5m
Work:
W=F
×∆
y=500N·m=500J
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This note was uploaded on 04/17/2008 for the course PHYS 2014 taught by Professor Nandi during the Spring '08 term at Oklahoma State.
 Spring '08
 Nandi
 Physics, Energy, Force, Kinetic Energy, Work

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