Question about cross and dot product

  • Thread starter leonne
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Homework Statement


There are two points p1 pointing up p2 pointing right


Homework Equations





The Attempt at a Solution


I need to find [tex]\stackrel{\rightarrow}{p1}[/tex] * r^

[tex]\stackrel{\rightarrow}{p2}[/tex] X p1^

[tex]\stackrel{\rightarrow}{p2}[/tex]* r^

they got [tex]\stackrel{->}{p1}[/tex] * r^ =0 why is that? i know if they are perpendicual than they =0 but not sure where r^ is pointing

[tex]\stackrel{->}{p2}[/tex] X p1^ =p2 well i know when 2 vectors are paralle the = 0 so i am guess when they are perpendicular they are p2 , but only one is a vector not sure if that matters.

[tex]\stackrel{->}{p2}[/tex]* r^ = p well i am guessing from this, that r^ is parallel with p2. thats why with p1 its 0, its perpendicular, but how do we find out which way r^ is pointing?

thxs
 

Answers and Replies

  • #2
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Homework Statement


There are two points p1 pointing up p2 pointing right
What do you mean that one "points up" and the other "points right"? A point doesn't have direction. Do you mean vectors?

Homework Equations





The Attempt at a Solution


I need to find [tex]\stackrel{\rightarrow}{p1}[/tex] * r^
What is r? Is r^ supposed to be a unit vector?
[tex]\stackrel{\rightarrow}{p2}[/tex] X p1^

[tex]\stackrel{\rightarrow}{p2}[/tex]* r^

they got [tex]\stackrel{->}{p1}[/tex] * r^ =0 why is that? i know if they are perpendicual than they =0 but not sure where r^ is pointing
If two vectors are perpendicular, their dot product is zero. The vectors themselves are not necessarily zero vectors.
[tex]\stackrel{->}{p2}[/tex] X p1^ =p2 well i know when 2 vectors are paralle the = 0 so i am guess when they are perpendicular they are p2 , but only one is a vector not sure if that matters.
If two vectors are parallel, then one is a scalar multiple of the other. Also, their cross product is the zero vector.
[tex]\stackrel{->}{p2}[/tex]* r^ = p well i am guessing from this, that r^ is parallel with p2. thats why with p1 its 0, its perpendicular, but how do we find out which way r^ is pointing?
Not much of what you wrote makes sense. Please include all of the given information for this problem.
 

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