Finding the perpendicular distance in this moments question

AI Thread Summary
The discussion focuses on finding the perpendicular distance in a mechanics problem involving forces and angles. Participants clarify that the distance labeled 'x' in the initial diagram is not the required measurement. Instead, the correct approach involves determining the perpendicular distance from point C to line BF, which is equivalent to length AF. After some calculations, the distance from C to BF is found to be 1.414 meters, leading to a moment calculation of 70.7 Nm when multiplied by the force of 50N. The conversation emphasizes the importance of accurately interpreting the geometry of the problem to arrive at the solution.
Bolter
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Homework Statement
See below
Relevant Equations
moment = force x perp dist
I have tried this question but can't get my head around to doing part b)

Screenshot 2020-10-18 at 15.30.36.png


This is the sketch I have drawn and I'm guessing 'x' is the distance that I have to fine that's perpendicular to force Fb, though I'm not sure if I have set it up correctly?

IMG_5380.JPG


Any help would be appreciated! Thanks
 
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Extend the dotted line of FB down and to the left. Drop a normal to this line starting at point A. Determine the length of this normal line.
 
Distance "x" of your drawing is not the one required to find.

Also, note that the angles of section AC and force Fb are the same.
A 45-degree inclined distance of 2 m separates both lines.
A perpendicular distance between those lines would be...
 
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Chestermiller said:
Extend the dotted line of FB down and to the left. Drop a normal to this line starting at point A. Determine the length of this normal line.
Lnewqban said:
Distance "x" of your drawing is not the one required to find.

Also, note that the angles of section AC and force Fb are the same.
A 45-degree inclined distance of 2 m separates both lines.
A perpendicular distance between those lines would be...

I redrew the diagram and and labelled the new perpendicular distance I have to find, however I don't think I have enough info in the question to be able to work out this distance unless I'm missing something?

IMG_5382.JPG
 
Bolter said:
I redrew the diagram and and labelled the new perpendicular distance I have to find, however I don't think I have enough info in the question to be able to work out this distance unless I'm missing something?

View attachment 271134
There is enough info. It might be more obvious if you show point C and consider the relationship between the line AC and the line of action of the force.
 
haruspex said:
There is enough info. It might be more obvious if you show point C and consider the relationship between the line AC and the line of action of the force.

I tried including line AC in my diagram but I don't see how it'd help me find any angles or lengths.
I thought I could somehow use Pythagoras theorem to the right angle triangle ABF (in my diagram) where I know AB is sqrt(10) but I still have 2 unknown sides so that won't work

IMG_5383.JPG
 
Bolter said:
I tried including line AC in my diagram but I don't see how it'd help me find any angles or lengths.
I thought I could somehow use Pythagoras theorem to the right angle triangle ABF (in my diagram) where I know AB is sqrt(10) but I still have 2 unknown sides so that won't work

View attachment 271140
What is the distance from C to BF? This is what @Lnewqban was hinting at in post #3.
 
haruspex said:
What is the distance from C to BF? This is what @Lnewqban was hinting at in post #3.

By that do you mean the perpendicular distance from C to BF which is equivalent to length AF as they are parallel to each other?

EDIT: Ok I got distance from C to BF to be 1.414m and assuming that's equal to AF then AF = 1.414m
hence moment is 1.414m * 50N = 70.7Nm
 
Last edited:
Bolter said:
By that do you mean the perpendicular distance from C to BF which is equivalent to length AF as they are parallel to each other?

EDIT: Ok I got distance from C to BF to be 1.414m and assuming that's equal to AF then AF = 1.414m
hence moment is 1.414m * 50N = 70.7Nm
Right.
 
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