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Homework Help: Magnitude of Displacement :P

  1. Oct 17, 2004 #1
    Okay i dont have the best physics teacher :-/ he often gets confused with what he's teaching and shows us the wrong thing...We have four problems for homework and I would just like one of you experts to check over it ;)

    1. A car is driven 125 km due west, then 65 km due south. What is the magnitude of displacement? R^2=a^2 + b^2
    R^2=125^2 + 65^2
    R=140.9 (about)
    2. A shopper walks from the door of the mall to her car 250m down a lnae of cars, then turns 90 degrees to the right and walks an additional 60m. What is the magnitude of the displacement of her car from the mall door?
    R^2=a^2 + b^2
    R^2=60^2 + 250^2
    R=257.1 (about)
    3. A hiker walks 4.5 km in one direction, then makes a 45 degree turn to the right and walks another 6.4 km. What is the magnitude of her displacement?
    R^2= a^2 + b^2 - 2ab COS(angle)
    R^2= 4.5^2 + 6.4 ^2 -2(4.5)(6.4)cos45
    R^2=20.25 + 40.96- 40.729
    R=4.526 (about)
    4. What is the magnitude of your displacement when you follow directions that tell you to walk 225 m in one direction, make a 90 degree turn to the left and walk 350 m, then make a 30 degree turn to the right and walk 125 m?
    I'm not sure how to go about doing this one but what I DO know is
    how the triangle looks and the angle measurements. I'm just not
    sure what it is I'm supposed to be writing down. A hand plz lol?
  2. jcsd
  3. Oct 17, 2004 #2
    ...would I use the first or second equation? What about a combination of both? ...maybe its a trick question lol maybe its right there you just have to know what it is...
  4. Oct 17, 2004 #3
    You could use both. Get the resultant magnitude (R1) from the first two directions. And then find the resultant (R2) from R1 and the 3rd vector.
  5. Oct 17, 2004 #4
    thanks! is the rest of it right?
  6. Oct 17, 2004 #5
    isnt the resultant vector 125??? whoaaa...*confused*
  7. Oct 17, 2004 #6
    To find the resultant magnitude I would use r2=a2+b2 rite? i dont know what youre talking about the next part that confuses me..3rd vector is 125 correct?
  8. Oct 17, 2004 #7
    please someone help my gpa is plummeting thru tha ground ive made 2 awful homework grades recently: 71% and a 76%!!!! :'(
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