Physics

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The mass of the sign shown is 28.5 kg. Find the weight supported by (a) the left support and (b) the right support.

Between the left and right support is 0.900m and from the right support to the end of the sign is 0.300m.

------------------------------
| | --------> (0.900m)|| --->(0.300m)

I got answers: a. 111.1 and b. 186.2 but I'm not sure if they're correct. Can someone please help?

  • Physics -

    Weight of the sign is W = mg = 28.5kg•9.8m/s² = 297.3N
    The sum the moments around the left bottom of the sign.
    Clockwise moment Mcw = 297.3N • (1.2m/2) = 167.6 N•m
    Counterclockwise moment Mccw = F•0.9m
    That is, the cw rotation of the sign about the left corner is resisted by a support force.
    F = 167.6N•m / 0.9m = 186.2N ← in the right column

    The left support can be determined in a similar fashion, or simply by noting that it must support the remaining vertical force:
    Left F = W - Fr = 297.3N - 186.2N = 111.1N ← left support

  • Physics -

    28.5x9.80 = 279.3 not 297.3.
    therefore the left support would equal 93.1 not 11.1

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