Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Projectile motion (am I on drugs?)

  1. Jan 26, 2008 #1
    [SOLVED] Projectile motion (am I on drugs?)

    1. The problem statement, all variables and given/known data
    I can't believe how much time I have spent on this.
    Picture4-1.png


    2. Relevant equations
    Constant acceleration



    3. The attempt at a solution
    Here is the data I am using to solve for
    [itex]V_a[/itex]
    [itex]x_0=0[/itex],
    [itex]x_f=30[/itex],
    [itex]y_0=7[/itex],
    [itex]y_f=10[/itex],
    [itex]a_y=-g=-32.2[/itex],
    [itex]V_{0y}=V_a\sin30[/itex],
    [itex]V_{0x}=V_a\cos30[/itex]

    From x direction:
    [tex]\Delta X=V_{0x}t\Rightarrow t=\frac{30}{V_a\cos30}[/tex]


    From y direction:
    [tex]\Delta Y=V_{oy}+.5a_yt^2[/tex]
    [tex]\Rightarrow 3= V_a\sin30*(\frac{30}{V_a\cos30})-16.1[\frac{30}{V_a\cos30}]^2[/tex]

    [tex]\Rightarrow 3=30\tan30-16.1*(\frac{40}{V_a})^2[/tex]

    Which gets me a negative under the radical!
     
  2. jcsd
  3. Jan 26, 2008 #2
    seriously I am about to lose it. i have been over this like ten times!
     
  4. Jan 26, 2008 #3
    Where's the negative under the radical? 40 and [tex]V_a[/tex] are both positive, right? ...
     
  5. Jan 26, 2008 #4
    How'd you get that "40" under the radical, anyway?? I get 34.64 ...
     
  6. Jan 26, 2008 #5
    Oh wow. I better look into that drugs thing. The solution is 36.7 but I am getting 42.2. But then again, I'm on drugs. So let me check again.

    Thanks B.
     
  7. Jan 26, 2008 #6
    Yeah, your right Bells (mind if I call ya Bells?). I'm cooked this semester. Thanks for the help.

    Casey
     
  8. Jan 26, 2008 #7
    Happens to the best of us ... keep at it.
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook