louey (cal2859) – Ch6HW3 – forin – (56930)
1
This printout should have 15 questions.
Multiplechoice questions may continue on
the next column or page – Fnd all choices
be±ore answering.
001 (part 1 of 2) 10.0 points
A twodimensional ±orce
v
F
=
F
x
ˆ
ı
+
F
y
ˆ
moves
a particle to a new location that is
vr
=
r
x
ˆ
ı
+
r
y
ˆ
±rom where it was originally located. I±
F
x
= 1 N,
F
y
=
−
1 N,
r
x
= 1 m, and
r
y
=
2 m, what is the work done on the particle by
the ±orce?
Correct answer:
−
1 J.
Explanation:
The work is given by
W
=
v
F
·
Δ
=
F
x
r
x
+
F
y
r
y
= (1 N) (1 m) + (
−
1 N) (2 m)
=
−
1 J
.
002 (part 2 of 2) 10.0 points
²ind the angle between
v
F
and
.
Correct answer: 108
.
435
◦
.
Explanation:
Since
W
=
v
F
·
Δ
=
v
v
v
v
F
v
v
v

Δ

cos
θ
θ
= cos
−
1
W
v
v
v
v
F
v
v
v

Δ

.
v
v
v
v
F
v
v
v
=
r
F
2
x
+
F
2
y
=
r
(1 N)
2
+ (
−
1 N)
2
= 1
.
41421 N
and

Δ

=
r
r
2
x
+
r
2
y
=
R
1 m
2
+ 2 m
2
= 2
.
23607 m
,
so
θ
= cos
−
1
b
−
1 J
(1
.
41421 N) (2
.
23607 m)
B
=
108
.
435
◦
.
003 (part 1 of 6) 4.0 points
A lithium nucleus has mass 5
.
1
×
10
−
27
kg. I±
its speed is 0
.
988
c
(that is,
V/c
= 0
.
988), what
is the particle energy? Use
c
= 3
×
10
8
m
/
s.
Correct answer: 2
.
97176
×
10
−
9
J.
Explanation:
The particle energy is just the total energy,
given by
E
=
γ m c
2
.
So we have
E
=
1
±
1
−
p
V
c
P
2
m c
2
=
1
R
1
−
0
.
988
2
(5
.
1
×
10
−
27
kg)
c
2
=
2
.
97176
×
10
−
9
J
.
004 (part 2 of 6) 4.0 points
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 (part 3 of 6) 4.0 points
What is the kinetic energy?
Correct answer: 2
.
51276
×
10
−
9
J.
Explanation:
The kinetic energy is given by
KE
=
E
−
E
rest
= 2
.
97176
×
10
−
9
J
−
4
.
59
×
10
−
10
J
=
2
.
51276
×
10
−
9
J
.
006 (part 4 of 6) 4.0 points
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View Full Documentlouey (cal2859) – Ch6HW3 – forin – (56930)
2
Next, an electric Force acts on the lithium
nucleus and does 4
.
7
×
10
−
9
J oF work on the
particle. Now what is the particle energy?
Correct answer: 7
.
67176
×
10
−
9
J.
Explanation:
We simply add the work done on the system
to the total energy From beFore:
E
f
=
E
i
+
W
= 2
.
97176
×
10
−
9
J + 4
.
7
×
10
−
9
J
=
7
.
67176
×
10
−
9
J
.
007 (part 5 of 6) 4.0 points
What is the rest energy now?
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 Spring '08
 Turner
 Energy, Force, Potential Energy, Correct Answer, kef, Ry, Esys

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