In the diagram on the right, a plank weighing 120 N is supported by two trestles at points A and B. A man weighing 480 N is standing on the plank. a Redraw the diagram, showing all the forces acting on the plank. b Calculate the total clockwise moment of the two weights about A. c Use the principle of moments to calculate the upward force from

Elements Of Electromagnetics
7th Edition
ISBN:9780190698614
Author:Sadiku, Matthew N. O.
Publisher:Sadiku, Matthew N. O.
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Section: Chapter Questions
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clockwise moment =
anticlockwise moment
Centre of mass
= x X N 0
100 N x 2 m
essentials
%3D
Although weight is distributed
through an object, it acts as a
single, downward force from a
So: the counterbalance should be placed 0.5 m from O.
b Let F be the maximum load (in N). With this load on the crane, the
counterbalance must produce its maximum moment about O. So it must
be the greatest possible distance from 0- in other words, 1 m from it. As
the crane is in equilibrium, the principle of moments applies:
Taking moments about O:
clockwise moment =
point called the centre of mass
(or centre of gravity).
For an object to be stable when
resting on the ground, its centre
of mass must be over its base. If
an object is pushed, and its
centre of mass passes beyond
anticlockwise moment
400 N X 1 m
Fx 2 m
%3D
the edge of its base, it will
F = 200 N
%3D
topple over.
ment l
balan
So: the maximum load is 400 N.
os pe
९SNO
1 In the diagram on the right, a plank weighing 120 N is supported by
two trestles at points A and B. A man weighing 480N is standing on
2m-
centre of
mass
the plank.
a Redraw the diagram, showing all the forces acting on the plank.
b Calculate the total clockwise moment of the two weights about A.
c Use the principle of moments to calculate the upward force from
of plane
weight
of man
weight
of plank
= 120 N
A
B.
the trestle at B.
d What is the total downward force on the trestles?
e What is the upward force from the trestle at A?
f The man now walks past A towards the left-hand end of the plank.
What is the upward force from the trestle at B at the instant the plank starts to tip?
2 In Testing the principle of moments on the opposite page, moments were taken about X. Calculate the moments
again, only about point Y. Are the sums of the clockwise and anticlockwise moments still equal?
g How far is the man from A as the plank tips?
Related topics: balanced forces 2.06; moments and equilibrium 3.01; centre of mass 3.02
Transcribed Image Text:clockwise moment = anticlockwise moment Centre of mass = x X N 0 100 N x 2 m essentials %3D Although weight is distributed through an object, it acts as a single, downward force from a So: the counterbalance should be placed 0.5 m from O. b Let F be the maximum load (in N). With this load on the crane, the counterbalance must produce its maximum moment about O. So it must be the greatest possible distance from 0- in other words, 1 m from it. As the crane is in equilibrium, the principle of moments applies: Taking moments about O: clockwise moment = point called the centre of mass (or centre of gravity). For an object to be stable when resting on the ground, its centre of mass must be over its base. If an object is pushed, and its centre of mass passes beyond anticlockwise moment 400 N X 1 m Fx 2 m %3D the edge of its base, it will F = 200 N %3D topple over. ment l balan So: the maximum load is 400 N. os pe ९SNO 1 In the diagram on the right, a plank weighing 120 N is supported by two trestles at points A and B. A man weighing 480N is standing on 2m- centre of mass the plank. a Redraw the diagram, showing all the forces acting on the plank. b Calculate the total clockwise moment of the two weights about A. c Use the principle of moments to calculate the upward force from of plane weight of man weight of plank = 120 N A B. the trestle at B. d What is the total downward force on the trestles? e What is the upward force from the trestle at A? f The man now walks past A towards the left-hand end of the plank. What is the upward force from the trestle at B at the instant the plank starts to tip? 2 In Testing the principle of moments on the opposite page, moments were taken about X. Calculate the moments again, only about point Y. Are the sums of the clockwise and anticlockwise moments still equal? g How far is the man from A as the plank tips? Related topics: balanced forces 2.06; moments and equilibrium 3.01; centre of mass 3.02
clockwise moment =
anticlockwise moment
Centre of mass
= x X N 0
100 N x 2 m
essentials
%3D
Although weight is distributed
through an object, it acts as a
single, downward force from a
So: the counterbalance should be placed 0.5 m from O.
b Let F be the maximum load (in N). With this load on the crane, the
counterbalance must produce its maximum moment about O. So it must
be the greatest possible distance from 0- in other words, 1 m from it. As
the crane is in equilibrium, the principle of moments applies:
Taking moments about O:
clockwise moment =
point called the centre of mass
(or centre of gravity).
For an object to be stable when
resting on the ground, its centre
of mass must be over its base. If
an object is pushed, and its
centre of mass passes beyond
anticlockwise moment
400 N X 1 m
Fx 2 m
%3D
the edge of its base, it will
F = 200 N
%3D
topple over.
ment l
balan
So: the maximum load is 400 N.
os pe
९SNO
1 In the diagram on the right, a plank weighing 120 N is supported by
two trestles at points A and B. A man weighing 480N is standing on
2m-
centre of
mass
the plank.
a Redraw the diagram, showing all the forces acting on the plank.
b Calculate the total clockwise moment of the two weights about A.
c Use the principle of moments to calculate the upward force from
of plane
weight
of man
weight
of plank
= 120 N
A
B.
the trestle at B.
d What is the total downward force on the trestles?
e What is the upward force from the trestle at A?
f The man now walks past A towards the left-hand end of the plank.
What is the upward force from the trestle at B at the instant the plank starts to tip?
2 In Testing the principle of moments on the opposite page, moments were taken about X. Calculate the moments
again, only about point Y. Are the sums of the clockwise and anticlockwise moments still equal?
g How far is the man from A as the plank tips?
Related topics: balanced forces 2.06; moments and equilibrium 3.01; centre of mass 3.02
Transcribed Image Text:clockwise moment = anticlockwise moment Centre of mass = x X N 0 100 N x 2 m essentials %3D Although weight is distributed through an object, it acts as a single, downward force from a So: the counterbalance should be placed 0.5 m from O. b Let F be the maximum load (in N). With this load on the crane, the counterbalance must produce its maximum moment about O. So it must be the greatest possible distance from 0- in other words, 1 m from it. As the crane is in equilibrium, the principle of moments applies: Taking moments about O: clockwise moment = point called the centre of mass (or centre of gravity). For an object to be stable when resting on the ground, its centre of mass must be over its base. If an object is pushed, and its centre of mass passes beyond anticlockwise moment 400 N X 1 m Fx 2 m %3D the edge of its base, it will F = 200 N %3D topple over. ment l balan So: the maximum load is 400 N. os pe ९SNO 1 In the diagram on the right, a plank weighing 120 N is supported by two trestles at points A and B. A man weighing 480N is standing on 2m- centre of mass the plank. a Redraw the diagram, showing all the forces acting on the plank. b Calculate the total clockwise moment of the two weights about A. c Use the principle of moments to calculate the upward force from of plane weight of man weight of plank = 120 N A B. the trestle at B. d What is the total downward force on the trestles? e What is the upward force from the trestle at A? f The man now walks past A towards the left-hand end of the plank. What is the upward force from the trestle at B at the instant the plank starts to tip? 2 In Testing the principle of moments on the opposite page, moments were taken about X. Calculate the moments again, only about point Y. Are the sums of the clockwise and anticlockwise moments still equal? g How far is the man from A as the plank tips? Related topics: balanced forces 2.06; moments and equilibrium 3.01; centre of mass 3.02
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