practice 11 – ALIBHAI, ZAHID
1
Latest unpenalized work: Apr 8 2007 Sunday
04:00 (after this date you can not make a
perfect score). Work cutoff: Apr 8 2007, 4:00
am.
Question 1
part 1 of 1
10 points
Two weights attached to a uniform beam
of mass 38 kg are supported in a horizontal
position by a pin and cable as shown in the
figure.
The acceleration of gravity is 9
.
8 m
/
s
2
.
23 kg
20 kg
2
.
9 m
8 m
37
◦
38 kg
What is the tension in the cable which sup
ports the beam?
Answer in units of kN.
Question 2
part 1 of 3
10 points
A uniform rod pivoted at one end “point
O
” is free to swing in a vertical plane in a
gravitational field.
However, it is held in
equilibrium by a force
F
at its other end.
x
y
ℓ
F
F
x
F
y
W
R
x
R
R
y
θ
O
Force vectors are drawn to scale.
What
is
the
condition
for
translational
equilibrium along the horizontal
x
direction?
1.
F
x
= 0
2.

R
x
+
F
x
= 0
3.
R
x

F
x
cos
θ
= 0
4.
R
x

F
x
sin
θ
= 0
5.
F
x
cos
θ

R
x
sin
θ
= 0
Question 3
part 2 of 3
10 points
What
is
the
condition
for
translational
equilibrium along the vertical
y
direction?
1.
R
y
+
F
y

W
= 0
2.
R
y

F
y
+
W
= 0
3.
R
y
+
F
y
= 0
4.
R
y
sin
θ
+
F
y
sin
θ

W
cos
θ
= 0
5.
W

R
y
+
F
y
= 0
Question 4
part 3 of 3
10 points
Taking the origin (point
O
) as the pivot
point, what is the condition for rotational
equilibrium?
1.
F
y
ℓ
sin
θ

W
ℓ
2
sin
θ

F
x
ℓ
sin
θ
= 0
2.
F
y
ℓ
cos
θ

W
ℓ
2
cos
θ

F
x
ℓ
sin
θ
= 0
3.
2
F
y
ℓ
sin
θ

W ℓ
cos
θ

2
F
x
ℓ
sin
θ
= 0
4.
W
ℓ
2

F
x
ℓ
cos
θ

F
y
ℓ
cos
θ
= 0
5.
F
y
ℓ
cos
θ

W ℓ
sin
θ
+
F
x
ℓ
sin
θ
= 0
Question 5
part 1 of 1
10 points
A light string has its ends tied to two walls
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practice 11 – ALIBHAI, ZAHID
2
separated by a distance equal to fourfifth the
length
L
of the string as shown in the figure.
A 25 kg mass is suspended from the center of
the string, applying a tension in the string.
The acceleration of gravity is 9
.
8 m
/
s
2
.
4
L
5
25 kg
L
2
L
2
θ
θ
What is the tension in the two strings of
length
L
2
tied to the wall?
Answer in units of N.
Question 6
part 1 of 1
10 points
A solid bar of length
L
has a mass
m
1
. The
bar is fastened by a pivot at one end to a
wall which is at an angle
θ
with respect to the
horizontal. The bar is held horizontally by a
vertical cord that is fastened to the bar at a
distance
x
cord
from the wall.
A mass
m
2
is
suspended from the free end of the bar.
T
m
2
m
1
θ
x
cord
L
Find the tension
T
in the cord.
1.
T
=
parenleftbigg
m
1
+
1
2
m
2
parenrightbigg parenleftbigg
L
x
cord
parenrightbigg
g
cos
θ
2.
T
=
parenleftbigg
m
1
+
1
2
m
2
parenrightbigg parenleftbigg
L
x
cord
parenrightbigg
g
3.
T
= (
m
1
+
m
2
)
parenleftbigg
L
x
cord
parenrightbigg
parenleftBig
g
2
parenrightBig
4.
T
=
parenleftbigg
1
2
m
1
+
m
2
parenrightbigg parenleftbigg
L
x
cord
parenrightbigg
g
cos
θ
5.
T
= (
m
1
+
m
2
)
g
cos
θ
6.
T
=
parenleftbigg
m
1
+
1
2
m
2
parenrightbigg parenleftbigg
L
x
cord
parenrightbigg
g
sin
θ
7.
T
=
parenleftbigg
1
2
m
1
+
m
2
parenrightbigg parenleftbigg
L
x
cord
parenrightbigg
g
sin
θ
8.
T
= 0
9.
T
=
parenleftbigg
1
2
m
1
+
m
2
parenrightbigg parenleftbigg
L
x
cord
parenrightbigg
g
10.
T
= (
m
1
+
m
2
)
g
sin
θ
Question 7
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 Spring '08
 Turner
 Force, Friction, Mass, Work, Zahid, ZAHID Question

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