One more Vector problem and we are good to go!!!

[junior_J]

The Problem:
Find the change in velocity of a yacht if it changes its velocity from
5ms^-1 due north to 3ms^-1 due west and also state its direction.

The solution :
(resultant vel.)^2 = 5^2 + 3^2 = 5.8 ms^-1
direction = tan-1(3/5) = 31 degrees west of north

However , the books answer is 5.8 ms^-1 in a direction 31 degrees west of south . what am i doing wrong here ???

[radou]

Draw down the vectors and it should become clear why the direction is 31 degrees west of south. Btw, the change equals \vec{v}_{2}-\vec{v}_{1}.

http://upload.wikimedia.org/wikipedia/commons/thumb/5/5b/Vector_subtraction.png/217px-Vector_subtraction.png

[junior_J]

I did draw it but unless south means up and norths means down on paper I dont know what ur getting at lolz I wanna tear my book apart !!!!!!

[junior_J]

err .... got it !!! im so embarrased !!!

thank you !!! :)

[radou]

I did draw it but unless south means up and norths means down on paper I dont know what ur getting at lolz I wanna tear my book apart !!!!!!

\vec{v}_{1} is pointing north (up). \vec{v}_{2} is pointing west (left). \vec{v}_{2}-\vec{v}_{1} is then pointing south-west.