Help with vector diagrams (1 Viewer)

[cricketfan1997]

Hi.
Two vehicles each travelling at 20ms^-1, approach an intersection. Car A approaches from south, car b from east, what is the velocity of b relative to a.

The answer is 28ms^-1 SW. I can get the 28ms^-1, but i cant get the south west, the only rule i know is head to tail.

Thanks, if you could show me what the vector diagram is and why it is not something else (head to tail could have many variations, how do you know which particular diagram it is. like head to tail could produce an angle of south east as well?)

 

[Kurosaki]

u use vector subtraction

|<-----
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V

 

[cricketfan1997]

why? please reply i have a test in 2 hrs

 

[Kurosaki]

M8, you should have learnt it at school or from a textbook.....
A approaches from south, hence heading north
B approaches from east, hence heading west.

so A is like
^
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B is like <---------

Velocity of B relative to A= B-A= B+(-A)

B is <--------------
-A is
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v
Then u add them