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M2 - Moments

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Need help on Question 5d and 6.

For 5c I got R as square root of 17W at 14.04 degrees (rounded).

I don't know how to get 5d :/ Answer says 82.9 degrees, but don't know how to get it.

And for question 6, I get F as 285N. But don't know what to do next.

Your help would be appreciated!

Thanks
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ttoby
15
For 5d, take moments about point B. You'll get an equation involving W, l, sin(theta) and cos(theta). Cancel out as many terms as you can, then rearrange into the form sin⁡θcos⁡θ=something\frac{\sin\theta}{\cos\theta}=something then use the fact that tan⁡θ=sin⁡θcos⁡θ\tan\theta=\frac{\sin\theta}{ \cos \theta}.

For 6, you could probably take moments about the end of the ladder that's touching the wall. Use the value of F that you calculated, and an unknown position for the person on the ladder, and make clockwise moments equal anticlockwise moments, and solve to find the position of the person on the ladder.

(by the way I haven't verified the calculations you've already done)
I don't have anything constructive to add to the thread but was wondering if you had the mark scheme for those questions. :biggrin:

And if so, could you post it on this thread?


Cheers

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