Why use unit vector for this, and not for that?

[viet_jon]

the car problem in my text uses the unit vector, and the second one doesn't...

how come?

 

[Delphi51]

The second problem is more complex and requires vectors to take care of the 3 directions involved. The first (car) problem has only one direction so no need for vectors.

 

[viet_jon]

but it did the opposite of just that.

the car used 'unit' vector...

while the second does not use the 'unit' vector

 

[mplayer]

The first problem is asking for a moment about an axis. I'm pretty sure this is why you have to employ the unit vector in your calculations. If i recall correctly (been awhile since I was in statics) the unit vector here will be j or [0i 1j 0k]. Is that familiar?

The second problem is asking for a moment about a point.