1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

How do you derive the correct projectile motion formula?

  1. Feb 2, 2013 #1
    1. The problem statement, all variables and given/known data
    A jaguar(A) leaps from the origin at a speed of v0 = 6 m/s and an angle β = 35° relative to the incline to try and intercept the panther(B) at point C. Determine the distance R that the jaguar jumps from the origin to point C. given the the angle of the incline is θ = 25°.




    2. Relevant equations

    a = dv/dt

    3. The attempt at a solution

    I know how to solve this problem by just looking up the constant acceleration formula and translating the velocity and R into cosines and sines. My question is, How do we know that we have to derive the equation s = s_0 +v_0(t) +.5a(t^2)? When I first tried it, and since it was trying to relate velocity and distance I thought I would use the derivation a = (dv/dx)(dx/dt) = v(dv/dx). Once I integrated it out I got a(x - x_0) = (v^2)/2 - (v_0^2)/2... why doesn't this work for solving the problem? How do you know from the beginning that you're going to have to use the general form I showed above when we are not given any info about time in the problem statement? Let me know if I need to clarify my question at all.
     
  2. jcsd
  3. Feb 2, 2013 #2

    mfb

    User Avatar
    2016 Award

    Staff: Mentor

    You do not have to, but it is useful.

    How does the height-dependence of the velocity help?

    Experience. In doubt, use the general formula.
     
  4. Feb 2, 2013 #3
    Thanks for the reply! Do we always have to use the general form for projectile motion since it is 2-D. I now kind of think we do, because we are going to need a way to relate the equations in both directions, so we are going to have to use a form with time because thats the variable that is the same in both directions, is that correct? Does that make sense?
     
  5. Feb 2, 2013 #4

    mfb

    User Avatar
    2016 Award

    Staff: Mentor

    There are always multiple methods to solve the problem, but that one is the easiest.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: How do you derive the correct projectile motion formula?
Loading...