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# M1 Moments

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1. For part A i drew my diagram and put the weight W just to the right of point C
the distance between C and W i called x

i did this calculation
2W+xW=4T
2T+xW=0

Taking them away from each other gives 2W-2T=4T
2W=6T

xW+2()=0
xW+=0
x=

so does that mean that actually x is m to the left of C?
2. (Original post by Steelmeat)

For part A i drew my diagram and put the weight W just to the right of point C
the distance between C and W i called x

i did this calculation
2W+xW=4T
2T+xW=0

Taking them away from each other gives 2W-2T=4T
2W=6T

xW+2()=0
xW+=0
x=

so does that mean that actually x is m to the left of C?
You should get but it should be from B and non-negative.
3. (Original post by Cryptokyo)
You should get but it should be from B and non-negative.
The reason for this is that your equations should be
as moments act in different directions.

As the sum of the anticlockwise moments = sum of clockwise moments.
4. (Original post by Cryptokyo)
You should get but it should be from B and non-negative.
i don't quite understand? i've subbed the equation for t in terms of w back into the equation where i took moments about C
5. Your walking is all correct apart from the sign errors in the moments.
6. (Original post by Steelmeat)
i don't quite understand? i've subbed the equation for t in terms of w back into the equation where i took moments about C
When you take moments about a point the anticlockwise moments are equal to the clockwise moments. The weight of the rod acts clockwise and the tension in the string acts anticlockwise when moments are taken about B. And the inverse is true for moments about C.
7. Hence the moments about B should be and about C should be
8. (Original post by Cryptokyo)
When you take moments about a point the anticlockwise moments are equal to the clockwise moments. The weight of the rod acts clockwise and the tension in the string acts anticlockwise when moments are taken about B. And the inverse is true for moments about C.
yea

taking moments about B weight w acts clockwise = tension in the string which is anticlockwise

.... so i'm right then?
9. (Original post by Steelmeat)
yea

taking moments about B weight w acts clockwise = tension in the string which is anticlockwise

.... so i'm right then?
You are correct in way but your answer is negative as your equations give due to sign errors in the moments it should be that and that
10. (Original post by Cryptokyo)
Hence the moments about B should be and about C should be
?????????

no when you take moments about something you don't include the moment about itself....
11. Zacken sort me out fam
12. (Original post by Steelmeat)
Zacken sort me out fam
(Original post by Steelmeat)
2T+xW=0
Why are you saying that tension and weight are acting in the same direction?
13. (Original post by Zacken)
Why are you saying that tension and weight are acting in the same direction?
Yes they both act clockwise, i put the little arrow acting up the string for tension is that wrong?
14. (Original post by Steelmeat)
Yes they both act clockwise, i put the little arrow acting up the string for tension is that wrong?
So tension acts vertically upwards and weight acts vertically downwards but they both produce a clockwise moment... what?
15. (Original post by Zacken)
So tension acts vertically upwards and weight acts vertically downwards but they both produce a clockwise moment... what?
yes lemme post a pic of my diagram

Edit: i'm gonna redraw it since it's a bit messy
16. (Original post by Steelmeat)
yes lemme post a pic of my diagram

Edit: i'm gonna redraw it since it's a bit messy
Don't bother dude. Put your rule parallel to the plank. Now push push the ruler vertically upwards, does it turn anticlockwise or clockwise?

Now push the ruler vertically downwards, does it turn anticlockwise or clockwise?
17. (Original post by Zacken)
Don't bother dude. Put your rule parallel to the plank. Now push push the ruler vertically upwards, does it turn anticlockwise or clockwise?

Now push the ruler vertically downwards, does it turn anticlockwise or clockwise?
pushing on the left hand side of the ruler pushing upwards turns the ruler clockwise

pushing vertically down on the right hand side of the ruler turns it clockwise also
18. (Original post by Steelmeat)
pushing on the left hand side of the ruler pushing upwards turns the ruler clockwise

pushing vertically down on the right hand side of the ruler turns it clockwise also
Oh, you've put the weight to the right of C. Urgh.

So that means that the centre of mass is 2/3 to the left of C, yes.

So the distance from A is 1 + 2 - (2/3) = 7/3.
19. (Original post by Zacken)
Oh, you've put the weight to the right of C. Urgh.

So that means that the centre of mass is 2/3 to the left of C, yes.

So the distance from A is 1 + 2 - (2/3) = 7/3.
Oh i see thanks for sorting this out
20. (Original post by Zacken)
x.
How do i do part C?

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