What error was made in calculating the moment at point H?

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The discussion centers on the calculation of moments at point H in a physics problem involving forces and angles. The user initially calculated the moment as -RCos(theta)(0.4) + 60(0.2) = 0, leading to Rcos(theta) = 30. However, the correct approach, as per the mark scheme, requires taking moments at point R, resulting in Rcos(theta) = 60. The error lies in neglecting the moment due to the horizontal component of R at point H.

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For figure 1.2, if you take moments at the point where H acts, then you get (assuming moments are positive anti-clockwise):

-RCos(theta)(0.4) + 60(0.2) = 0

Rearranging gives:

Rcos(theta) = 30

However, according to the mark scheme (which takes moments at the point where R acts) Rcos(theta) = 60

What have I done wrong?
 
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About H, there is also a moment due to the horizontal component of R.
 
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