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121. We use Eq. 820.
(a) The force at
x
= 2.0 m is
(17.5 J) ( 2.8 J)
4.9 N.
4.0 m 1.0 m
dU
F
dx
−−
−
=−
≈−
=
−
(b) The force points in the +
x
direction (but there is some uncertainty in reading the graph
which makes the last digit not very significant).
(c) The total mechanical energy at
x
= 2.0 m is
Em
v
U
=+
≈
−
−
=
−
1
2
1
2
20
15
77
55
22
(.)
( .)
.
.
in SI units (Joules). Again, there is some uncertainty in reading the graph which makes
the last digit not very significant. At that level (–5.5 J) on the graph, we find two points
where the potential energy curve has that value — at
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This note was uploaded on 05/17/2011 for the course PHY 2049 taught by Professor Any during the Spring '08 term at University of Florida.
 Spring '08
 Any
 Physics, Force

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