1. Apr 24, 2010

### Angello90

1. The problem statement, all variables and given/known data
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)?

2. Relevant equations
M= r x F

3. The attempt at a solution
I did the quesion, but I'm not sure if it's correct. Can anyone check it for me?

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2. Apr 24, 2010

### 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.

3. Apr 24, 2010

### 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)

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• ###### QL Mql.jpg
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4. Apr 26, 2010

### Angello90

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