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Rev. 2
REVIEW SHEET #4:
Work; Kinetic & Potential Energy; Energy Conservation
Definitions:
Work
(a scalar)
is the scalar product of force and displacement
cos
W
F d
F d
θ
=
•
=
⋅
⋅
r
r
r
r
(The above expression applies to cases where the force is constant.)
W=0 unless there is a displacement component parallel to the force direction.
Work can
be positive (if θ is between 0 and 90°) or negative (if θ is between 90° and 180°).
The total work done on an object by all of the external forces acting on that object is
equal to the work done by the net external force:
(
29
ext
total
W
F
d
=
•
∑
r
r
Kinetic Energy
(a scalar)
2
1
2
K
mv
=
(m=mass, v=velocity; K is never negative)
Work – Kinetic Energy Theorem:
the total work done on an object by all external
forces is equal to the change in the object’s kinetic energy:
total
final
initial
W
K
K
K
= ∆
=

Gravitational Potential Energy
(a scalar)
:
U
g
= mgy
(m=mass, y=height above
a reference level; this expression applies near the earth’s surface where g is constant
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 Spring '08
 KOHLER
 Physics, Energy, Force, Potential Energy, Work

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