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Homework Help: Projectile motion (clueles)

  1. Feb 18, 2007 #1
    1. The problem statement, all variables and given/known data
    A jet fighter of mass 3t climbs from ground level to a height of 10,000m
    in one minute. At that time it has a horizontal component of velocity
    of 241m/s and a vertical component of velocity of139m/s. find
    (A) the direction in which it is travelling
    (B) the speed
    (C) its kinetic enregy
    (D) its increase in gravitational potential energy
    (E) the power delivered by its engines during the climb

    2. Relevant
    I've only been doing this for 3 weeks now, and i get some of it
    but dont get most.
    anyhelp would be nice..., i get that theres alot.
    but im sure its basic stuff, im not looking for answers
    just help.

    3. The attempt at a solution

    My attempt

    a) tan = Vx/Vy
    =30 degrees

    just a tidbit, i know that tan(29.96 =0.5767 But how do i get 0.5767 to = 29.96?)

    b) V²=Vy²+Vx²
    =278.2121 m/s

    The answers said it = 27.8m/s, why?

    the next three are where i
    have even less of an idea.

    c) KE=½mv² right
    =417318.15j, but thats too high,right?

    the answer book said it =1.16x108j , which
    freaked me out because what is with the
    x? where did that come from!

    d) is it to do with PE=mgh? cause i did that, but no go

    e) righteo.

    (sorry for any spelling errors)
    Last edited: Feb 18, 2007
  2. jcsd
  3. Feb 18, 2007 #2


    User Avatar
    Staff Emeritus
    Science Advisor

    You have [itex]\tan\theta=0.5967 \Rightarrow \theta=\tan^{-1}(0.5967)[/itex]

    I don't know you've got the tan there. The correct equation is V2=Vy2+Vx2. Hence, V2=77402, and thus V=√(77402)

    Incidentally, is the bit I've highlighted in blue a typo, and should read 278?

    Why do you think that? It is incorrect though, since you used the value for v instead of the value for v2

    This means T=1.16x108=116000000


  4. Feb 18, 2007 #3
    Oh, the tan was a mistake
    & im a goob, i didn't get that T=1.16x108=116000000
    stuff makes more sense, cheers.
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