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Homework Help: What are the two possibilities for its x component?

  1. Oct 9, 2005 #1
    HELP ASAP--vectors

    You are given a vector in the xy plane that has a magnitude of 90.0 units and a y component of -55.0 units.

    a) what are the two possibilities for its x component?

    b) assuming the x component is known to be positive, specify the vector which, if you add it to the original one, would give a resultant vector that is 80.0 units long and points entirely in the -x direction.

    I have no idea how to do this. I thought I did it correctly but now I'm not so sure.

    if you could do this step by step that would be great. Don't get too high tech on me though because you will confuse me more and I won't get what you're saying. lol.

    I saw someone with a similar problem but she got part a and I didn't.

    thanks a ton. :tongue:
    Last edited: Oct 9, 2005
  2. jcsd
  3. Oct 9, 2005 #2
    For a) it's just sqrt(-55^2 + x^2) has to add up to 90. Solve for x, then since it's the magnitude (absolute value), it can be either + or - x

    B) Says x is positive, so that would be the first answer you get in part a). Now you want to make a vector that cancels out with the Y component (makes it 0). You can setup a simple equation like you do in the first part or just look at it and see the answer. Also the new vector needs to add to the x component to make it 90. So same thing.
    Last edited: Oct 9, 2005
  4. Oct 9, 2005 #3

    Okay so I DID do part a right...good-Thanks.

    but part b, I have (71.24,-55) to (-80,0) [I made a typo earlier, it's not 90 units long, it's 80.0, sorry). that's right I know but I don't get what equation to use after that? :uhh:
  5. Oct 9, 2005 #4
    You don't really need any equations, you can just break it up into components and do some algebra.

    (x1,y1) + (x2,y2) = (x3,y3) or (72.5, -55) + (x2,y2) = (-80,0)

    and for that you just add the components (x + x2 = x3 and y + y2 = y3).
  6. Oct 9, 2005 #5

    okay i get that. so i got (-151.24, 55). is that how i'd leave the answer? "since it says specify the vector.." is there a different form i should put it in?
  7. Oct 9, 2005 #6
    That should be good. Only other thing you could do is draw em.
  8. Oct 9, 2005 #7
    thank you so much, you're amazing.

    i only have one other problem i don't get but whatever.
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