A-Level Maths: S1-06 Moments: Total Moment of Forces on a Lamina 1

[harrisonp]

Hello there, can i give all moments as positive values but state the clockwise or anticlockwise direction, or is this forbidden? Thank you.

[jessicayu.]

My teacher uses clockwise as positive and anticlockwise as negative. If we write this down telling the examiner which way we are using pos and neg, will the answer still be correct? For example, for part b, my answer as 50Nm instead of -50Nm.

Thank you.

[echok]

Does it matter which moment you calculate for part B first?

[nasirzahir]

Hi, in an mei practice paper today I came across a lamina question where there were forces acting on all sides, some of which were unknown, and the mark scheme simply resolved horizontally and vertically to find the unknowns. I thought it was necessary to take moments since the lamina was a square, rigid body - please help me understand where I'm going wrong

[Possiblyqiqi]

If i wanted to find the moment about a point outside the rectangle, let’s say 5m to the right of D, how would that be calculated?

I feel like it would be the same as point O since it’s not affecting the corners, but I’m not sure. Can you please explain?

[jamminermit]

I’m not sure if I’m just clutching at straws here, but for finding the total moment force about O, you get the correct answer by adding up the total moment force at each of the four corners (so -80-50+30+0=-100Nm) and then dividing the result by the number of corners, giving -100/4 = -25Nm. Just wondering if this is a coincidence and whether it is generalised to a lamina with 5 points, or n points?