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Homework Help: Vectors i/j

  1. Apr 6, 2008 #1
    1. The problem statement, all variables and given/known data
    A motorist drives south at 24.0 m/s for 3.00 min, then turns west and travels at 25.0 m/s for 3.00 min, and finally travels northwest at 30.0 m/s for 1.00 min. For this 7.00 min trip, find the following values.
    a. Total vector displacement displacement
    b. Average speed
    c. average velocity



    2. Relevant equations



    3. The attempt at a solution

    a. Δr=24m/s(180s)south+25m/s(180s)west+30m/s(60s)north west

    =4320m(-j)+4500m(-i)+1272.8(-i)+1272.8j Would this "j" be positive or negative?
    =-5772.8i-3047.208

    square root ((-5772.8)^2+(-3047.208)^2)=6527.680

    θ=tan-1(3047.208/5772.8) or would it be tan-1(3047.208/5772.8)
    =27

    b. average speed=4320+4500+1800
    1062/7(1/60)=
    25.286

    c. Would the average velocity direction be the same as the one from part a?

    Thank you very much
     
  2. jcsd
  3. Apr 6, 2008 #2
    a. yes you got it correct. that j should be positive since he is going north at that moment.
    b. the average speed is also correct. another quicker way to get it is a weighted mean of the 3 speed.
    c. yes the direction should be that of a. it means the total displacement per over total time.
     
  4. Apr 7, 2008 #3
    Thank you very much

    Regards
     
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