lavallo (jhl936) – Homework 12 – florin – (58140)
1
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printout
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have
8
questions.
Multiplechoice questions may continue on
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before answering.
001
(part 1 of 2) 10.0 points
The coefficient of friction is
μ
from A to B,
and B to E is frictionless. Block
m
1
is pushed
down the ramp and released at A with velocity
v
1
and is accelerating down. Let
E
=
K
+
U
= mechanical energy
vector
P
= momentum
A
B
C
D
E
m
1
m
2
What is conserved as
m
1
goes from A to B?
1.
vector
P
2.
Both
E
and
vector
P
3.
Neither
E
nor
vector
P
correct
4.
E
Explanation:
Because there is friction, energy is dissi
pated and mechanical energy is not conserved.
Because there is gravity as well as friction and
the net force is not zero since it is accelerating
down, momentum is not conserved.
002
(part 2 of 2) 10.0 points
What is conserved as the masses
m
1
+
m
2
slide
together from D to E?
1.
Neither
E
nor
vector
P
2.
vector
P
3.
Both
E
and
vector
P
4.
E
correct
Explanation:
Because there is no friction between the
track and the masses, the mechanical energy
E
is conserved.
But the total momentum
vector
P
is not conserved because the magnitude and
direction of the velocity of the masses change
due to the gravity and the normal force by the
track.
003
10.0 points
A triangular wedge 8 m high, 12 m base
length, and with a 14 kg mass is placed on
a frictionless table. A small block with a 9 kg
mass (and negligible size) is placed on top of
the wedge as shown in the figure below.
14 kg
12 m
8 m
9 kg
Δ
X
wedge
14 kg
12 m
8 m
9 kg
All surfaces are frictionless, so the block
slides down the wedge while the wedge slides
sidewise on the table. By the time the block
slides all the way down to the bottom of the
wedge, how far Δ
X
wedge
does the wedge slide
to the right?
Correct answer: 4
.
69565 m.
Explanation:
Let :
M
= 14 kg
,
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lavallo (jhl936) – Homework 12 – florin – (58140)
2
m
= 9 kg
,
L
= 12 m
,
and
H
= 8 m
.
Consider the wedge and the block as a two
body system.
The
external forces
acting on
this system — the weight of the wedge, the
weight of the block and the normal force from
the table — are all vertical, hence the net
hor
izontal momentum
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 Spring '10
 Florin
 Force, Friction, Mass, Correct Answer, kg, m/s

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