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Muddy Card Responses Lecture M6
Can you reexplain why there's a moment now? (see picture)
N
5 m
A
B
C
20 0
10 m
Not sure
what the question is. Here are a couple of thoughts. The reaction at A and B
are force reactions (but not pure moments). However, the force of 200N has a moment
about both points A and B, so the reaction force at A must have a moment about B that is
equal and opposite to that due to the load, and similarly for the moment due to the
reaction at A and the load about point B.
In the section method, why is the moment arm for F
ED
L
?
See figure below. The
moment arm of F
ED
about B is the height of point E about the bar AB, which is a length
L. This represents the perpendicular distance of the line of action of the force F
ED
from
point B.
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View Full DocumentCould you explain which moments you used in the last example?
See picture above.
By taking moments about point B, we eliminate F
EB
and F
AB
, which both pass through
point B and therefore have no moment arm about it. The only two forces
acting on the
section which have a moment about B are F
ED
(which we want to find) and the reaction at
point A, of P.
Not quite clear on the end of the last example why are we taking moments around
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 Winter '12
 CharlesColeman
 Aeronautics, Astronautics

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