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A large logAB is 6 m long. It rests in a horizontal position on two smooth supports C and D, whereAC = 1 m and BD = 1 m, as shown in Figure . David needs an estimate of the weight of the log, but the log is too heavy to lift off both supports. When David applies a force of magnitude1500 Nvertically upwards to the log at A, the log is about totilt about D.

(a) State the value of the reaction on the log at C for this case.

... 0....

David initially models the log as uniform rod. Using this model,

(b) estimate the weight of the log

[ I got 3750 N for this]

The shape of the log convinces David that his initial modelling assumption is too simple. Heremoves the force at A and applies a force acting vertically upwards at B. He finds that the log is about to tilt about C when this force has magnitude1000 N. David now models the log as a non-uniform rod, with the distance of the centre of mass of the log from C as x metres. Using this model, find

(c) a new estimate for the weight of the log,

im absolutely stuck here... the way ive laid it out is;

Moments at D => 1500x5 =W(4-x)

Moments at C => 1000x5 =????

then... ???

I dont know what to do...

(d) the value of x.

Any help would be appreciated. :)

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# Homework Help: Mechanics Question III

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