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# M2 Moments question Watch

1. The question is as follows:

"A uniform rectangular hatch ABCD, of mass 12 kg, is hinged along its edge AB, and is horizontal when closed. A vertical force acting upwards through the mid-point of CD keepas the hatch open at a fixed angle. Assuming the weight of the hatch acts through the centre of ABCD, find the magnitude of the vertical force."

I tried to look side-on and do weight acting at angle theta to the horizontal (the hatch) and force acting at angle theta to the perpendicular of the hatch, and it ended up as W cos theta = F cos theta, suggesting that F = 12g which is wrong apparently. What am I doing wrong?
2. Nope, nevermind, I figured out what I did wrong; just me being stupid and forgetting that this chapter is called MOMENTS and thus the question probably involves moments. Forgot they were different length from the pivot, and I then factored that in and got the right answer of 6g (58.8 N).

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Updated: December 19, 2010
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