madrid (tmm2353) – HW 63 – Antoniewicz – (56445)
1
This
printout
should
have
14
questions.
Multiplechoice questions may continue on
the next column or page – find all choices
before answering.
001(part1of2)4.0points
A mass of 0
.
15 kg hangs from a vertical spring
in the lab room.
You grab hold of the mass
and throw it vertically downward. The speed
of the mass just after leaving your hand is
3
.
41 m
/
s
.
While the mass moved downward a distance
of 0
.
07 m, how much work was done on the
mass by the Earth? Use
g
= 9
.
8 m
/
s
2
.
Correct answer: 0
.
1029 J.
Explanation:
We can write
W
Earth
=
vector
F
·
Δ
vectorr
=
(
0
,
−
m g,
0
) · (
0
,
Δ
y,
0
)
= (0
.
15 kg)(9
.
8 m
/
s
2
)(3
.
41 m
/
s)
=
0
.
1029 J
.
002(part2of2)4.0points
The
speed
of the
mass
has
decreased
to
2
.
89 m
/
s.
How much work was done on the
mass by the spring?
Correct answer:
−
0
.
3486 J.
Explanation:
We can write
Δ
KE
=
W
spring
+
W
Earth
⇒
W
spring
= Δ
KE
−
W
Earth
=
1
2
m
vextendsingle
vextendsingle
vectorv
f
vextendsingle
vextendsingle
2
−
1
2
m

vectorv
i

2
−
W
Earth
=
−
0
.
3486 J
.
003(part1of6)2.0points
A lithium nucleus has mass 5
.
1
×
10

27
kg. If
its speed is 0
.
992
c
(that is,
v/c
= 0
.
992), what
is the particle energy? Use
c
= 3
×
10
8
m
/
s.
Correct answer: 3
.
63599
×
10

9
J.
Explanation:
The particle energy is just the total energy,
given by
E
=
γ m c
2
.
So we have
E
=
1
radicalBigg
1
−
parenleftbigg
v
c
parenrightbigg
2
m c
2
=
1
radicalbig
1
−
0
.
992
2
(5
.
1
×
10

27
kg)
c
2
=
3
.
63599
×
10

9
J
.
004(part2of6)2.0points
What is the rest energy?
Correct answer: 4
.
59
×
10

10
J.
Explanation:
The rest energy is just
E
rest
=
m c
2
= (5
.
1
×
10

27
kg)
c
2
=
4
.
59
×
10

10
J
.
005(part3of6)2.0points
What is the kinetic energy?
Correct answer: 3
.
17699
×
10

9
J.
Explanation:
The kinetic energy is given by
KE
=
E
−
E
rest
= 3
.
63599
×
10

9
J
−
4
.
59
×
10

10
J
=
3
.
17699
×
10

9
J
.
006(part4of6)2.0points
Next, an electric force acts on the lithium
nucleus and does 4
.
3
×
10

9
J on the particle.
This preview has intentionally blurred sections. Sign up to view the full version.
View Full Document
This is the end of the preview.
Sign up
to
access the rest of the document.
 Fall '08
 Turner
 Energy, Mass, Correct Answer, Antoniewicz

Click to edit the document details