Vector Direction Help: Solving a Vector Problem with Given Direction and Length

[teffy3001]

ive been trying to do this problem but i don't know where to start...any help?


let v be a vector of length 9 in the direction 65degrees south of west.

if u has the same direction as v, and if 3|u| = 2|v|, then which of the following can be used to describe u?


u = 5.705i + 12.235j
u = -2.536i - 5.438j
u = 2.536i + 5.438j
u = -5.705i - 12.235j
none of these

 

[radou]

none of these

Are you sure about that?

 

[teffy3001]

no I am not sure...cause I am not even sure how to get started on this question...

 

[radou]

no I am not sure...cause I am not even sure how to get started on this question...

Draw your vector v down, first. Do you know anything about projections on the x and y axis?

 

[teffy3001]

yeah
i think i have to find the components of u but using the magnitude of v..is that right?

 

[radou]

yeah
i think i have to find the components of u but using the magnitude of v..is that right?

First of all, you have to write down v in the form v = ___ i + ___ j. Then, you know that 3|u| = 2|v|, eg |u| = 2/3|v|.

 

[teffy3001]

okay thanks i think i got it now : )