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Homework Help: Projectile motion with aerodynamic drag force

  1. Oct 5, 2011 #1
    1. The problem statement, all variables and given/known data

    A projectile of mass 1300kg is launched from the ground (x =0, y =0)
    initial velocity components Vx=Vy=108m/s
    aerodynamic drag force is of magnitude C(V)^2
    where C = 0.6

    2. Relevant equations

    Finding the range and angular momentum initial and final

    3. The attempt at a solution
    1. I found V = 152.74 (*by V= root(Vx^2 + Vy^2)
    2. and weight as 12753 kg
    3. I tried to find aerodynamic drag force (FD), but I got something like 13997.70 m^2/s^2
    (it should be in Newtons right?)
    4. I think I'll break FD to x and y components and use them to calculate when it'll reach it's peak (Vy= 0) and based on it I'll use the the t to get the distance...but how to find it?
    5. for the angle, can I assume that it was 45 degrees angle?
    since Vx=Vy?
    6. and I have no idea how to find the angular momentum @.@

    Sorry if my working is quiet "useless" cause I'm quiet "blind" at this subject...

    Thanks before :D

  2. jcsd
  3. Oct 5, 2011 #2


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    Staff Emeritus
    Science Advisor
    Gold Member

    This question is not a trivial one and indeed, cannot be solved analytically in terms of elementary functions. You can however, solve the system numerically.

    As you say, you need to apply Newton's second law to each component (horizontal and vertical) of the motion. This will then yield a system of two coupled differential equations that you will need to sole numerically.

    As I said, this problem isn't straightforward and the fact that you have posted this in the Introductory Physics forums would suggest that you are still in elementary physics classes. So I must as, are you sure that you have the question correct? How much numerical analysis have you done?
  4. Oct 5, 2011 #3
    yes, I'm sure that the question is correct @.@
    I found the V and the W... but can't go any further than that @.@
    so should I post this question in advance physics section?
  5. Oct 5, 2011 #4


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    Staff Emeritus
    Science Advisor
    Gold Member

    Have you tried to write down the two PDEs from Newton's Second law?

    I think that your question is fine here, but I can move it for you if you wish.
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