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Homework Help: Vector Dynamics

  1. Oct 7, 2011 #1
    1. The problem statement, all variables and given/known data

    An air craft has an initial velocity of 90(i+ j)ms-1and a final velocity of 10(10i + 10j +3k) ms-1. The time taken for this change to occur is 100 s. Determine the:
    a)average velocity for the 100 s period.
    b)average speed for the period.
    c)constant acceleration of the airplane in unit vector notation.
    d)magnitude of the acceleration.
    e)vertical height the plane has risen.
    f)distance plane travelled for the 100 s period

    2. Relevant equations

    3. The attempt at a solution

    I have calculated all the above but i am confused as to which one of the vectors to state as the variable.

    using the formula S= ut + 0.5at^2

    i got the unit vector form (9500i + 9500j+ 1500k) this is correct.

    now the solution says the vertical height is 1500k, but i thought 9500j was the vertical component. can some please explain this to me.

    my answer
    1. The problem statement, all variables and given/known data

    2. Relevant equations

    3. The attempt at a solution
  2. jcsd
  3. Oct 7, 2011 #2


    User Avatar

    Staff: Mentor

    I think you must be picturing the x-y-z axes as representing, let's say, x for eastward, y for up (as in altitude), and z for northward? That could feasibly be true, but for the velocity here rising to 100i + 100j + 30k it would be more like a ride on fighter plane, gaining 100m in altitude for every 104m you travel over terrain. If you instead interpret z as representing altitude, then plane passengers will be less terrified. :smile:

    I'm not saying I'm correct, but it seems the question does leave this up to you to decide. Which means there is room for ambiguity.
    Last edited: Oct 7, 2011
  4. Oct 7, 2011 #3
    thanks, i was kinda thinking along those lines too...
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