What is the moment about point C?

[Angello90]

Homework Statement

Find the moment about the origin of a vector of magnitude 100 units acting from
A=(2, 0, 4) to B=(5, 1, 1). What is the moment about the point C=(−1, 2, 1)?

Homework Equations

M= r x F

The Attempt at a Solution

I did the quesion, but I'm not sure if it's correct. Can anyone check it for me?

 

[HallsofIvy]

The "moment of a vector about a point" is the magnitude of the vector times the length of a line segment from the given point perpendicular to the line of the vector.

Since the vector acts "from (2, 0, 4) to (5, 1, 1)", its line of direction is given by x= 3t+ 2, y= t, z= -3t+ 4. You need to find the distance from (0, 0, 0) to that line and from (-1, 2, 1) to that line . Then multiply those by 100.

 

[Angello90]

So I need to find |OL| where O = (0, 0, 0) and L = (2+3t, t, 4-3t), thus

Making a moment of

Simillary to Q = (-1, 2, 1)

 

[Angello90]

Ahhh come on guys help me out here! Any hints?