louey (cal2859) – Ch6HW2 – florin – (56930)
1
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printout
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18
questions.
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before answering.
001(part1of4)10.0points
An object at location
(−
20
,
0
,
0
)
m moves to
location
(−
26
,
0
,
0
)
m.
While it is moving it
is acted on by a constant force of
(
25
,
0
,
0
)
N.
How much work is done on the object by this
force?
Correct answer:
−
150 J.
Explanation:
W
=
vector
F
·
Δ
vectorr
=
F
x
Δ
x
+
F
y
Δ
y
+
F
z
Δ
z
= (25
N
)(
−
26
−
(
−
20))m
=
−
150
002(part2of4)10.0points
Does the kinetic energy of the object increase
or decrease?
1.
There is no change in the kinetic energy
of the ball.
2.
Decrease
correct
3.
Increase
Explanation:
Consider the update form of the Conserva
tion of Energy:
E
sys,f
=
E
sys,i
+
W
surr
. The
system is the object, and the surroundings
are doing work on the object. The calculated
work due to the force on the object is neg
ative.
This means that the initial energy of
the system is greater than the final energy of
the system, i.e. the energy of the system de
creased.
The force acts on the object in a
direction that opposes the initial motion of
the object.
Thus, the kinetic energy of the
object decreases.
003(part3of4)10.0points
Now,
consider
a
different
object
as
it
moves from location
(−
26
,
0
,
0
)
m to location
(−
20
,
0
,
0
)
m. While it is moving, it is acted
on by a constant force of
(
25
,
0
,
0
)
N.
How
much work is done on the second object by
this force?
Correct answer: 150 J.
Explanation:
W
=
vector
F
•
Δ
vectorr
=
F
x
Δ
x
+
F
y
Δ
y
+
F
z
Δ
z
= (25
N
)(
−
20
−
(
−
26))m
= 150
004(part4of4)10.0points
Does the kinetic energy of the second object
increase or decrease?
1.
Decrease
2.
Increase
correct
3.
There is no change in the kinetic energy
of the ball.
Explanation:
Apply the update form of the Conservation
of Energy once again. The work calculated is
positive, so the final energy state will have a
greater value than the initial energy state.
005
10.0points
An electron traveling through a curving wire
in an electric circuit experiences a constant
force of 5
×
10
−
19
N, always in the direction
of its motion through the wire.
How much
work is done on the electron by this force as
it travels through 0
.
2 m of the wire?
Correct answer: 1
×
10
−
19
J.
Explanation:
Since the force and displacement are in the
same direction, the dot product reduces to a
simple scalar product:
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louey (cal2859) – Ch6HW2 – florin – (56930)
2
W
=
vector
F
·
Δ
vectorr
=
F
Δ
r
= (5
×
10
−
19
N)(0
.
2 m)
=
1
×
10
−
19
J
.
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 Spring '08
 Turner
 Conservation Of Energy, Energy, Force, Mass, Potential Energy

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