Lecture 16
pls16.1
Applications of the Work Energy Theorem / Power
Media: 1.
Tennis Ball
1.
WorkEnergy Theorem, Reformulated
(1)
Æ
If an object has an initial
i
KE
and some net work is done on the
object, then its
KE
increase (or decrease) equals the net work done on
the object.
Sometimes
net
W
is due to both conservative and nonconservative forces,
NC
C
net
W
W
W
+
=
(2)
Now we learned last time that
(3)
If we substitute this into eqn. (2) for
C
W
, we get
(
)
NC
i
f
net
W
PE
PE
W
+
−
−
=
,
and then substituting this into eqn. (1) for
net
W
gives us
(
)
NC
i
f
i
f
W
PE
PE
KE
KE
+
−
−
=
Æ
(
)
(
)
NC
i
i
f
f
W
PE
KE
PE
KE
+
+
=
+
(4)
(
)
i
f
C
PE
PE
W
−
−
=
net
i
f
W
KE
KE
+
=
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Lecture 16
pls16.2
and because the total mechanical energy
PE
KE
ME
+
=
we have
(5)
Æ
If an object has an initial
i
ME
and some nonconservative
work is
done on the object, then its
ME
increase (or decrease) equals the
nonconservative work done on the object.
Notice the similarity of eqn. (5) and eqn. (1).
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 Fall '11
 KODERA
 Physics, Energy, Force, Power, Work, WorkEnergy Theorem, Joule, KE, Wnet

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