Calculating Moment of Forces: Cartesian Vector Analysis for Column at Point A

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The discussion focuses on calculating the moment of forces about the base of a column using Cartesian vector analysis. The primary force given is F1 = 400i + 300j + 120k, and the moment is calculated using the equation M_A = r x F (summation). The user expresses confusion regarding the role of point E in their calculations and mentions consistently arriving at incorrect answers. They detail their approach of summing the cross products of forces with their respective distances, but the final moment calculation appears incorrect. The conversation highlights the challenges in vector analysis and the importance of correctly identifying all relevant points in the problem.
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I just realized this is in the wrong place..Move it to intro to physics please. Sorry

Homework Statement


Using Cartesian vector analysis determine the moment of the three forces about the base of the column at A. F1 =400i +300j+120k


Homework Equations



The x represents "cross"..i don't know the latex for it

M_a = r x F (summation)

The Attempt at a Solution



I keep getting the wrong answer and I think it has something to do with the point E. What does this have to do with anything?

What I am doing is summing all the forces crossed with their distances.

r_B={12k}N
r_{F3}={0i-j+8k}N

So M_A = (r_B x F_1) + (r_B x F_2) + (r_{F3} x F_3)
 

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M_A = {12k x 400i} + {12k x 300j} + {0i-j+8k x 120k}M_A = 4800k x -300j + 1440i x 8kM_A = -1440k^2 + 384k^2M_A = -1056k^2
 
Thread 'Variable mass system : water sprayed into a moving container'

Thread 'Variable mass system : water sprayed into a moving container'

Starting with the mass considerations #m(t)# is mass of water #M_{c}# mass of container and #M(t)# mass of total system $$M(t) = M_{C} + m(t)$$ $$\Rightarrow \frac{dM(t)}{dt} = \frac{dm(t)}{dt}$$ $$P_i = Mv + u \, dm$$ $$P_f = (M + dm)(v + dv)$$ $$\Delta P = M \, dv + (v - u) \, dm$$ $$F = \frac{dP}{dt} = M \frac{dv}{dt} + (v - u) \frac{dm}{dt}$$ $$F = u \frac{dm}{dt} = \rho A u^2$$ from conservation of momentum , the cannon recoils with the same force which it applies. $$\quad \frac{dm}{dt}...
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