Why is the moment along AB pointed in the negative y direction? why not positive how can you tell?
Why wouldn't it be pointed in the negative direction? It's all a matter of convention. Actually, it doesn't matter what you choose to be positive or negative, as long you apply the same convention to all moments and forces you're taking into account in a calculation.
i dont understand
It just means that they assumed a direction. If you work it out and and the answer for the moment is negative, then the moment was actually acting in the opposite direction.
WHY negative? why not positive then theres only 1 moment
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