Version One – Homework 7 – Heinz – 81204 – Oct 07, 2004
1
This
printout
should
have
14
questions.
Multiplechoice questions may continue on
the next column or page – find all choices
before answering.
The due time is Central
time.
Serway CP 05 76
08:05,
trigonometry,
numeric,
>
1
min,
wordingvariable.
001
(part 1 of 1) 10 points
A 2 kg block situated on a rough incline
with 37
◦
angle is connected to a spring of
negligible mass having a spring constant of
100 N
/
m.
The block is released from rest when the
spring is unstretched, and the pulley is fric
tionless.
The block moves 20 cm down the
incline before coming to rest.
The acceleration of gravity is 9
.
8 m
/
s
2
.
100 N
/
m
2 kg
μ
20 cm
37
◦
Find the coefficient of kinetic friction be
tween block and incline.
Correct answer: 0
.
114709 .
Explanation:
Given :
m
= 2 kg
,
θ
= 37
◦
,
k
= 100 N
/
m
,
and
Δ
x
= 20 cm
.
The work done by the friction force is
W
f
= (
f
x
cos 180
◦
) Δ
x
=

μ
k
n
Δ
x
=

μ
k
(
m g
cos
θ
) Δ
x
Applying the workkinetic energy theorem,
W
nc
=
W
f
= Δ
K
+ Δ
U
s
+ Δ
U
g
.
Since the block stars from rest and comes to
a stop,

μ m g
Δ
x
cos
θ
= 0 +
1
2
k
(Δ
x
)
2

m g
Δ
x
sin
θ .
Thus
μ
=

k
Δ
x
2
m g
cos
θ
+ tan
θ
=

(100 N
/
m) (0
.
2 m)
2 (2 kg) (9
.
8 m
/
s
2
) cos 37
◦
+ tan 37
◦
=

(0
.
638845) + (0
.
753554)
=
0
.
114709
.
Return to the Shuttle
09:01, trigonometry, numeric,
>
1 min, nor
mal.
002
(part 1 of 1) 10 points
A(n) 65 kg astronaut becomes separated from
the shuttle, while on a space walk. She finds
herself 50 m away from the shuttle and mov
ing with zero speed relative to the shuttle.
She has a(n) 0
.
65 kg camera in her hand and
decides to get back to the shuttle by throw
ing the camera at a speed of 12 m
/
s in the
direction away from the shuttle.
How long will it take for her to reach the
shuttle? Answer in minutes.
Correct answer: 6
.
94446 min.
Explanation:
Let :
M
= 65 kg
,
m
= 0
.
65 kg
,
d
= 50 m
,
and
v
= 12 m
/
s
.
Because of conservation of linear momentum,
we have
0 =
M V
+
m
(

v
)
m v
=
M V
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Version One – Homework 7 – Heinz – 81204 – Oct 07, 2004
2
where
V
is the velocity of the astronaut and
it has a direction toward the shuttle.
V
=
m v
M
=
(0
.
65 kg) (12 m
/
s)
65 kg
= 0
.
12 m
/
s
.
And the time it takes for her to reach the
shuttle
t
=
d
V
=
50 m
0
.
12 m
/
s
·
1 min
60 s
=
6
.
94446 min
.
Serway CP 06 59
09:01, trigonometry, numeric,
>
1 min, nor
mal.
003
(part 1 of 2) 5 points
A small block of mass 55 g is released from
rest at the top of a curved frictionless wedge
of mass 333 g which sits on a frictionless hori
zontal surface as shown.
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 Fall '09
 WOODAHL
 Physics, Kinetic Energy, Mass, Momentum, Work, kg, m/s

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