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hi, i have tried to work this question out it seems so easy but i must be missing something.

determine the magnitude and directional sense of the moment of the force at A about point O.

http://img229.imageshack.us/img229/9895/statics19hv.jpg [Broken]

these are 3 of my calculations for the question

F = 520 sin 30(6) - 520 cos 30(0)

F = 1560N or 1.56kN

also

F = 520 sin 120(6) - 0

F = 2.7kN

i also tried using vectors

r = {6i- 0j}m

F = {520sin30i - 520cos30j}N

= {260i - 450.33j}

The moment is therefore

Mo = r x F = 0i - 0j + [6(-450.33)-(0)(200)]k

= {-2.7k} kN.m

the answer in the books telling me 2.88 kN.m can someone point me to where I am going wrong i have obviously misunderstood something

thanks

determine the magnitude and directional sense of the moment of the force at A about point O.

http://img229.imageshack.us/img229/9895/statics19hv.jpg [Broken]

these are 3 of my calculations for the question

F = 520 sin 30(6) - 520 cos 30(0)

F = 1560N or 1.56kN

also

F = 520 sin 120(6) - 0

F = 2.7kN

i also tried using vectors

r = {6i- 0j}m

F = {520sin30i - 520cos30j}N

= {260i - 450.33j}

The moment is therefore

Mo = r x F = 0i - 0j + [6(-450.33)-(0)(200)]k

= {-2.7k} kN.m

the answer in the books telling me 2.88 kN.m can someone point me to where I am going wrong i have obviously misunderstood something

thanks

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