pandey (sp34566) – HW-18 – swinney – (57305)
1
This
print-out
should
have
22
questions.
Multiple-choice questions may continue on
the next column or page – find all choices
before answering.
001(part1of4)10.0points
Consider the diagram shown below.
003(part3of4)10.0points
What is the
z
component of the torque about
point A?

Given
r
= 4 m,
F
= 8 N and
θ
= 41
o
,

004(part4of4)10.0points
If the force were perpendicular to
vectorr
A
but the
answer is the same as in parts 1-3, what would
its magnitude be?

A
what is the
x
component of the torque about
the point A (choice of axes: +
x
to the right,
+
y
up, +
z
out of the page; origin at A)?
In this case,
vectorr
A
=
<
−
r
A
,
0
,
0
>
and
vector
F
new
=
<
0
, F
new
,
0
>,
so that
vector
τ
new
=
vectorr
A
×
vector
F
new
005
10.0points

=
(
0
,
0
,
−
r
A
F
sin
θ
)
=
(
0
,
0
,
−
(4 m)(8 N) sin 41
o
)
=
(
0
,
0
,
−
20
.
9939 N
·
m
)
002(part2of4)10.0points
What is the
y
component of the torque about
point A?
Which of the following is/are required for the
angular momentum of a system to be con-
stant?
I. Zero net external torque
II. Zero net energy transfer
III. Zero net external force

Explanation:
See Explanation 1.
3.
I only
correct

pandey (sp34566) – HW-18 – swinney – (57305)
2
4.
II,III only
7.
III only

006(part1of3)10.0points
A mass 4
.
6 kg is attached to a light cord,

which is wound around a pulley. The pulley is
a uniform solid cylinder of radius 6
.
8 cm and
mass 3
.
5 kg.
What is the magnitude of the net torque on
the system about the point on the axis at the
center of the pulley? The acceleration due to
gravity is 9
.
8 m
/
s
2
.
007(part2of3)10.0points

When the mass has a speed
v
= 26 m
/
s, the
pulley has an angular speed
ω
=
v
R
.
Determine the magnitude of the total an-
gular momentum of the system about a point
on the axis at the center of the pulley?