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Homework Help: Projectile and Resistance Force

  1. Apr 29, 2012 #1
    1. The problem statement, all variables and given/known data

    Consider a 10 kg projectile launched with an initial speed of 100 m/s at an angle of 35 degrees elevation. The Resistance force is R=-bv where b=10 kg/s. A) Use a numerical method to determine the horizontal and vertical positions of the projectile as a function of time. B) What is the range of the projectile? C) Determine the elevation angle that gives the maximum anle. (Hint: Adjust the elevation angle by the trial and error to find the greatest range).

    2. Relevant equations


    3. The attempt at a solution
    I am trying to come up with an equasion for part a, but I am getting confused. Could anyone help?

    I tried:
    I made a free body diagram with up being positive y direction and right being positive x direction.
    I set ƩFx= -(Vx)bv=mAx
    ƩFy= - mg - (Vy)bv=mAy
    I am not sure if this is right or where to go from here. Can someone help please and thank you.
  2. jcsd
  3. Apr 30, 2012 #2


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    Staff: Mentor

    Your resistance forces are ending up being multiplied by velocity twice. Probably not what you want :smile: I suggest you drop the "v" from bv in those terms.

    Note that they're asking you to use a numerical method. That implies some form of iterative process where the trajectory is computed in incremental steps with some discrete timestep Δt. This is called "integration" of the trajectory (related to what we usually think of as integration in Calculus).

    What types of trajectory integration methods have you come across?
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