Calculate angles from axis with a 3d vector

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  • #1
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Homework Statement



A vector is given by R(vector) = 1.90 ihat + 1.30 jhat + 2.92 khat.

Find the magnitude of the vector

Find the angle between the vector and the x, y, and z axis

Homework Equations



I have read something about dot product but im not sure if it applies here

The Attempt at a Solution



R(magnitude)=3.7183867

R(magnitude in xy plane)=2.302

R(magnitude in yz plane)=3.196

R(magnitude in xz plane)=3.484

I dont know if I should have solved for these or if i should try to solve for the angles in each plane specifically. I was just getting numbers to see where it got me.
 

Answers and Replies

  • #2
nicksauce
Science Advisor
Homework Helper
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Remember that for dot products
[tex]
\vec{u}\cdot\vec{v} = |u||v|\cos{\theta}[/tex]

Where theta is the angle between the vectors. So choose u = your vector R, and v = ihat, and you get the angle between R and the x-axis.
 
  • #3
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arent v(vector) and v(magnitude the same which follows for u. which means that it would just be cos( 0 ) b/c that is one
 
  • #4
diazona
Homework Helper
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arent v(vector) and v(magnitude the same which follows for u. which means that it would just be cos( 0 ) b/c that is one
Are you asking if [itex]\vec{v}[/itex] and [itex]|v|[/itex] (to use nicksauce's notation) are the same? They're not... [itex]\vec{v}[/itex] is a vector, while [itex]|v|[/itex] is a scalar. Completely different things. It's like the difference between an arrow and the length of the arrow.

Do you know how to take the dot product of two vectors?
 
  • #5
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no thats what im basically asking, we were not taught this but need to know it i guess to do this problem. Also it is not anywhere in the chapter's we are studying
 
  • #6
18
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I have to figure this out by tomorrow and i cant really figure out how to do it from looking up up anywhere. Can someone please resolve this one before it is due tomorrow?
 

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