Take the 2-minute tour ×
Physics Stack Exchange is a question and answer site for active researchers, academics and students of physics. It's 100% free.

I have to find to component of vector DE having magnitude 1 m .now the vector is in 4th quad making angle 90 degree with postive x axis The solution that my teacher showed is ax=1cos(270) .and ay = 1sin(270) ... Now my confusion is that if it makes 90 degree with x axis ....why not ax=1cos90 and ay=1sin90 .........my refrence shows ax=0 and ay=-1

share|improve this question

closed as off-topic by innisfree, Kyle Kanos, Kyle Oman, rob, John Rennie Jun 16 at 5:38

This question appears to be off-topic. The users who voted to close gave this specific reason:

  • "Homework-like questions should ask about a specific physics concept and show some effort to work through the problem. We want our questions to be useful to the broader community, and to future users. See our meta site for more guidance on how to edit your question to make it better" – innisfree, Kyle Kanos, Kyle Oman, rob, John Rennie
If this question can be reworded to fit the rules in the help center, please edit the question.

    
$\cos 90^o = \cos 270^o =0$. –  gonenc Jun 15 at 18:23
    
But sin90 is not equal to sin270 –  saiman qureshi Jun 15 at 18:25
    
Note that the angles are measured counter-clockwise with respect to the positive $x$ axis. –  gonenc Jun 15 at 18:26
    
Draw a picture - think why the angle might in fact be $-90^\circ$ or equivalently $270^\circ$. Something to do with those quadrants –  innisfree Jun 15 at 18:26
    
@innisfree: 4. quadrant $90^o$ means a unit vector pointing downwards in the $-y$ direction :) –  gonenc Jun 15 at 18:28

1 Answer 1

up vote 0 down vote accepted

Draw a picture...

enter image description here

From here the answer should be obvious. Don't focus just on the math - look at what is actually going on.

share|improve this answer
    
Thanx ,but i still dont understand how it works ,say we have to resolve a vector with magnitude 1 which lies in fourth quad (3,-4)...which is parallal to y axis ....what will be its angle with x axis –  saiman qureshi Jun 15 at 20:08
    
By convention we measure angles as I drew in my diagram: start at X axis and work counter clockwise. That makes the angle of the vector I drew 270°, and you get (0,-1) in vector notation $(\cos 270°, \sin 270°$) . The result is the same if you use an angle of -90° –  Floris Jun 15 at 20:11
    
Oh thanxs a lot ...i got you ..thanx a ton –  saiman qureshi Jun 15 at 20:17

Not the answer you're looking for? Browse other questions tagged or ask your own question.