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Homework Help: Year 11 motion/vector problem?

  1. Nov 14, 2008 #1
    1. The problem statement, all variables and given/known data
    I'm really not good at motion. It just doesn't seem to come easily to me, which is kind of disapointing, because physics is my favourite subject.

    Question: A body of mass 5kg is moving in a north easterly direction with a velocity of 28.3 m/s. If a westerly wind acts on it with a force of 73.5N what is the change in momentum after 8s.

    2. Relevant equations
    F = ma, a = v/s

    3. The attempt at a solution
    I figured i'd find the velocity of the force.
    F = ma
    73.5 = 5a
    a= 14.7

    a = v/t
    v = 14.7 * 8
    v = 117.6

    difference in p = m(v-u)
    p = 5(117.6-28.3)

    But this doesn't give the right answer. The answer is 588 N s East.

    I know i probably need to draw vectors and what not but the whole concept of vectors confuses me deeply. :(
    Could you explain to me how the diagram would work? Would i need to use non-right trig? And also, what am i doing wrong?
    I don't understand a lot of the concepts of vectors and motion, so try and explain it in the simplest way possible, because im not great at this stuff.

    Any help is appreciated. Thanks :)
  2. jcsd
  3. Nov 14, 2008 #2


    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper

    You need to think about velocity components for this one.

    The change in velocity is in the east/west direction. So what was the initial east/west velocity component?

    p.s. welcome to PF.
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