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Homework Help: Find magnitude of two velocities, with one at an angle?

  1. Sep 17, 2016 #1
    • Member advised to use the homework template for posts in the homework sections of PF.
    Here is the problem:

    I am sure I can use pythagorean theorem of quadratic equation to solve but to be honest I'm blanking ridiculously.
    I have tried setting it on a coordinate grid and finding the resultant, but I have had no luck! I know I've done this problem before in highschool but I'm blanking and have spent a few hours now contemplating this.
    Thank you!
  2. jcsd
  3. Sep 17, 2016 #2
    You could start by breaking up the wind into its x and y components. Remember your trig.
  4. Sep 17, 2016 #3
    Hi! I have tried what you said but still do not have the right answer. Here is my work:

    Excuse the writing, I'm in a car haha!
  5. Sep 17, 2016 #4
    Ok, so you found your components for the wind. Now find the components for the glider. look on your graph what angle is the glider traveling?
  6. Sep 17, 2016 #5
    Sorry, it looks like you already have the components for the resultant vector. So you should have no problem finding the magnitude by using Pythagorean theorem.
  7. Sep 17, 2016 #6
    Hi, as you can see I tried that. It did not work :( Do I sum both the x-coordinates? I had 31cos45 - 87 since they are on opposite sides of the coordinate grid.
  8. Sep 17, 2016 #7
    Ah, would it be at 180o?
  9. Sep 17, 2016 #8
    Right, what did that give you?
  10. Sep 17, 2016 #9
    Yes it would.
  11. Sep 17, 2016 #10
    92.037. I checked, not the right answer (for part a)
  12. Sep 17, 2016 #11
    I am getting a different answer. You have r^2 = (-65.08)^2 + (21.92)^2 ?
  13. Sep 17, 2016 #12
    Ah, my mistake. I redid it and got 68.67. I just checked and it is correct! Thank you! I will be able to solve for the angle :)
    I must have been too sloppy with the numbers, I realized my calculator was still keeping the negative number even while being squared, messing everything up.
    Thanks again!
  14. Sep 17, 2016 #13
    You're welcome!
  15. Sep 18, 2016 #14
    The problem also asks for the direction of the glider's ground track. (In your sketch, the directional sense of vector R is wrong.) It may help to draw the vectors to scale and connect them head to tail to get a preliminary ballpark resultant.
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