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    I never know what triangle to draw to resolve.
    In the attached image, would the horizontal vector be cos30*150 and vertical be sin30*150? I think I am wrong and there is no mark scheme for this questions. Or could the horizontal vector be cos30*3(since the weight of 150N is halfway along the ladder?). How do I know which one it is?
    Thanks in advance.

    EDIT: sorry guys, the question isn't the one on the actual photo. The question is as follows: state the values of the horizontal and vertical components of Q.
    Attached Images

    If you look at the question is says vertical wall so you know your vertical component is going to be the COS of the force and angle , the sin gives you the horizontal.

    I did it on paper if it helps, here is the picture! :P
    I'll add an explanation below the picture too.

    We need to analyse the situation first, so, try to note a key fact about the way we're handling the moments. We're not doing it along the bottom of the triangle, we're doing it along the side, we're handling the horizontal components and want them orthogonal to our axis-of-calculation or whatever you want to call it. We wont need the length though, as you'll guess :P

    So, work out horizontal W. I did a vector triangle to do it, so, slot in W as the vertical/adjacent, the angle being 30 degrees next to it, and then the horizontal force as the opposite, with the hypotenuse not being necessary. Tan of theta will equal the horizontal force due to the ladder divided by the ladders weight, this, weight * tan30 = horizontal aspect of W...

    Then just use the principle of moments, it's in equilibrium with the horizontal component of W twice as close to P than the horizontal component of Q is. Half your horizontal component for weight, and you end up with the answer I found.

    I hope I helped and that it's correct!

    ALSO you will want to open the image in another tab, the quality is bad on here for some reason, so, right click and open image in new tab from the address, and then zoom out! Sorry for the shiny ink, I love my fountain pen!
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Updated: February 11, 2017


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