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# M1 Mechanics - Forces at an angle (Edexcel) watch

1. (Original post by KiddingMe)
Would it be cos20 for this one then?
cos 20 or sin70; either.

Btw, is it better to have angles positive in these types of questions, to avoid errors when calculating?
I find it reduces errors if you make the angle between 0 and 90, sin/cos/tan are then all positive.
2. True, using CAST helps. Btw I changed the numbers in front of cos, but still not getting a diff answer.
3. (Original post by KiddingMe)
True, using CAST helps. Btw I changed the numbers in front of cos, but still not getting a diff answer.
A bit cryptic.

What do you currently get?
4. I got this:

I've a feeling, I messed up somewhere!
5. (Original post by KiddingMe)
I got this:

I've a feeling, I messed up somewhere!
Your 7.4N forces seems to have changed to 7N.

And for the other two forces you want sin75 and sin63
6. Just saw that 7! Getting sloppy here. Btw, why them 2 angles, wouldn't the ones I gave work (I guess not)!

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7. (Original post by KiddingMe)
Just saw that 7! Getting sloppy here. Btw, why them 2 angles, wouldn't the ones I gave work (I guess not)!

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Draw a little triangle.

With the first force (at A) you had sin70 (or cos 20). Same here. It's the sine of the angle the force makes with the line connecting it to the pivot point.
8. Sorry, I'm just confused now haha, could you draw your triangle that u used for one of the forces?

Edit: the sin75 and sin63 you gave, are the same as supplied in the actual question. Is this a coincidence, or simply we should've used them instead of all this complicated stuff!
9. (Original post by KiddingMe)
Sorry, I'm just confused now haha, could you draw your triangle that u used for one of the forces?
For the 2.9N force. Component perpendicular to the line from the pivot to the force.
Attached Images

10. Sorry Im just seeing what I just did v.wrong .... The 9.3N and 2.9N force should be resolved vertically while the 7.4N should be resolved only horizontally..right?
11. (Original post by KiddingMe)
Sorry Im just seeing what I just did v.wrong .... The 9.3N and 2.9N force should be resolved vertically while the 7.4N should be resolved only horizontally..right?
Yep. The direction perpendicular to the line connecting the force to the pivot.
12. Cool! I just drew out the triangles and it came out of the wash as -9.99Nm, which is same as the answer at the back!

Makes more sense now! Cheers unreservedly for all the help!

Btw, do you know any good revision material for these type of questions?
13. (Original post by KiddingMe)
Cool! I just drew out the triangles and it came out of the wash as -9.99Nm, which is same as the answer at the back!

Makes more sense now! Cheers unreservedly for all the help!
np

Btw, do you know any good revision material for these type of questions?
Sorry, can't help on that one, but others on here may have some useful suggestions.

Signing off the for the day. G.

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