banuelos (ojb93) – Homework 09 – florin – (58140)
1
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001
10.0 points
An object hangs motionless from a spring.
When the object is pulled down, the sum of
elastic potential energy of the spring and the
gravitational potential energy of the object
and Earth
1.
stays the same.
2.
decreases.
3.
increases.
correct
Explanation:
If released from its new position, the object
accelerates upward and passes the equilibrium
point with nonzero velocity.
The two forms
of potential energy are elastic potential en
ergy of the spring and gravitational potential
energy.
Even though the latter decreases as
the object is pulled down, the sum of the two
must increase for the object to be able to gain
kinetic energy.
002
10.0 points
A conservative force has the potential energy
function
U
(
x
), shown by the graph. A particle
moving in one dimension under the influence
of this force has kinetic energy 1.0 Joule when
it is at position
x
1
.
x
0
x
1
x
2
x
3
1
0
−
1
Position
Potential Energy (J)
Potential Energy
vs
Position
Which of the following is a correct state
ment about the motion of the particle?
1.
It moves to the left of
x
0
and does not
return.
2.
It oscillates with maximum position
x
2
and minimum position
x
0
.
correct
3.
It cannot reach either
x
0
or
x
2
.
4.
It moves to the right of
x
3
and does not
return.
5.
It comes to rest at either
x
0
or
x
2
.
Explanation:
The total energy of the particle is con
served, since only a conservative force acts
on it. So at any point on the axis,
V
(
x
) +
U
(
x
) =
V
(
x
1
) +
U
(
x
1
)
= 1
.
0 J + (
−
1
.
0 J)
= 0
,
V
(
x
) =
−
U
(
x
)
,
where
V
is the kinetic energy of the particle.
Since kinetic energy is bigger than or equal
to zero,
V
(
x
) =
−
U
(
x
)
≥
0
U
(
x
)
≤
0 J
so the particle oscillates between position
x
0
and
x
2
.
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 Spring '10
 Florin
 Energy, Potential Energy, Work

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