Danyal Education
Moments Assignment 3 (Pure)
Chapter
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Turning Effect of Forces
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Q:
State the principle of moments for a body in equilibrium.
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Q:
For a body to be in equilibrium, the sum of clockwise moments about any point is equal to the sum
of anti-clockwise moments about the same point.
Describe qualitatively the effect of the position of the centre of gravity on the stability of a simple
object resting on a level surface.
.
.
To increase the stability of an object, the centre of gravity should be as low as possible.
To increase the stability of an object, the centre of gravity should be as close to the centre of the
body as possible.
0cm
Ed
,
.6 Problems to Soh'e
1. A uniform metre beam is being balanced as shown below
20 cm
50
cm
90 cm
80 cm
al
IN
F
3N
5N
Calculate the sum of anti-clockwise moments about the pivoted point.
ny
( 3 marks )
Da
a.
b.
Calculate the sum of clockwise moments about the pivoted point in terms of
48
Chapter
F.
5
( 3 marks )
Turning Effect of forces
A uniform beam PQ is being balanced by the four forces shown.
40N
ati
o
2.
( 2 marks )
Apply the principle of moments to calculate F.
n
c.
l0N
P
----x
lm
----x
lm
uc
lm
F2
Ed
F
State the principle of moments.
( 2 marks )
b.
Calculate the force F1.
( 3 marks )
Da
ny
al
a.
c.
( 2 marks )
Calculate the force F,.
49
Chapter
5
Turning Effect of Forces
A spanner is used to release the bolt. The minimum moment required to turn the bolt is 20 Nm.
l0 cm
cm
A single force P1 is applied on the spanner at the position shown. What is the minimum force
required to turn the
the
c.
( 2 marks )
A second force F2 is applied together with F1 on the spanner at the position shown. Given that
for this case, both forces have the same magnitude, calculate the minimum force required to tum
bolt.
( 3 marks )
ny
al
b.
bolt?
Ed
u
a.
F2
ca
tio
F1
n
2O
What is the minimum length of spanner required to turn the bolt with a 20 N single force?
( 2 marks )
Da
3.
50
Chapter
5
Turning Effect of Forces
A wheelbarrow has a mass of 5 kg and contains 20 kg of rocks. The wheel touches the floor at
point C.
60 cm
Given that a force F of 100 N is required to lift the wheelbarrow at the handle as shown,
how far is the centre of gravity of the loaded wheelbarrow from point C? (Thke g to be 10 N/kg.)
( 4 marks )
al
Ed
uc
a.
cm
ati
40
on
4
b. In the absence of force F, the wheelbarrow rests on point C and point P. Suggest
stable.
two ways
( 2 marks )
Da
ny
which can easily make this loaded wheelbarrow more
5l
Chapter
5
Turning Effect of Forces
Misconceptions to Clarifr
The rectangular coil is rotated by vertical
A plane lamina is suspended freely from point
P. The weight of the lamina is 0.5 N and the
centre of gravity of the lamina is at C.
P
forces that act on sides ad and bc. The current
causes a constant force of 4.0 N on each side.
Given that ab is 10.0 cm and ad is 20.0 cm,
what is the maximum moment created on the
coil?
CI.
6.0 cm
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n
1
A 20Ncm
C 60Ncm
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B 40Ncm
D 80Ncm
(
)
A man walks along a 2 metre long weightless
beam towards a spring balance as shown
below. Given that the man's weight is 600 N,
ya
l E
du
ca
what is the distance between the man and the
spring balance when the spring balance shows
500 N?
The lamina is displaced to the position shown.
What is the moment that will cause the lamina
to swing?
A 3Ncm
B 4Ncm
C 5Ncm
D l2Ncm
action.
+
)
2m
The diagram below shows a d.c. motor in
A 0.33 m
C 1.09 m
4
B
D
0.91 m
1.67 m
()
A
man walks along a 2 metre long uniform
beam towards a spring balance as shown
below. Given that the weight of the man and
the beam are 600 N and 200 N respectively,
what is the distance between the man and the
Rotation
spring balance when the spring balance shows
500 N?
d
Da
n
2.
(
Spring balance
Spring balance
Commutator
+
R
Cell
A
C
52
0.33 m
1.33 m
B
D
0.67 m
t.6',7 m
Chapter
5
()
Turning Effect of forces
5.
The diagram below shows a uniform metre
ruler pivoted at the 30 cm mark but kept in
equilibrium by a 700 g mass suspended at the
0
20
uc
ati
on
20 cm mark.
100
30
a
700 g
What is the mass of the ruler?
A 1009
B 3509
C 7009
D 4900 g
Da
ny
al
Ed
()
53
Chapter
5
Turning Effect of forces