M2 Point C Moment Calculation: Why is it Not the Same as Book?

[werson tan]

Homework Statement

for M2 , if i take the moment at pont C , then my ans would be (0.3i) x ((125X(3/5) j +125(4/5) k )= 30j +22.5k
Which is not same with the book which use moment about D . why ? Is the value at the triangle at te upper part incorrect (circle part) ?

Homework Equations

The Attempt at a Solution

 

[paisiello2]

Picture is too small to read.

 

[werson tan]

Picture is too small to read.

 

[paisiello2]

Still too small. Just blow up the diagram.

 

[haruspex]

If you are taking moments about C then presumably you are considering the force at D. Isn't that in the direction -3/5j+4/5k? And should't the displacement vector be -3i?

 

[werson tan]

If you are taking moments about C then presumably you are considering the force at D. Isn't that in the direction -3/5j+4/5k? And should't the displacement vector be -3i?

Ya, I would ended up getting 22.5k +30j . But if I take moment about D , I would get 22.5j+30k... Is it correct?

 

[haruspex]

Ya, I would ended up getting 22.5k +30j . But if I take moment about D , I would get 22.5j+30k... Is it correct?

No, sorry, I had it wrong. The force at D is in the direction -4/5j+3/5k.