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!

Hard projectile motion problem

  1. Feb 5, 2005 #1
    A stone is projected from ground level at 80 m/s. Its speed when it reaches its highest point is 60 m/s.

    Find the angle of its projection. Answer in units of degrees.

    Lost count how many times i tried to get this one right.
     
  2. jcsd
  3. Feb 5, 2005 #2
    Post your working, so we can show you where you've gone wrong.
     
  4. Feb 5, 2005 #3
    OMG! i did it...it was my calculators fault! cant believe this.

    here try this if you have a ti-89 (set mode to degrees)
    (note the real values of the problem were 56m/s and 72m/s)

    solve(56 = 72 * cos(x), x)

    the answer it gives is weird

    x = 360. * ((weird symbole)n8 + .108173447969) or x = 360. * ((weird symbole)n8 - .108173447969)

    everything in my work made sense so i tried to do that manually:

    56/72 = 72/72 * cos(x)
    .77778 = cos(x)
    cos-1(.77778) = x
    x = 38.9


    Now the weird thing...putting this in calculator backwards with the value i determiend for theta:

    72 * cos(38.9) gets me 56! Freekin modern technology :yuck: lol

    o yea if anyone else wants to know how to do this problem, remember that in problems they neglect wind resistence the horizontal velocity is constant...so at the projectiles heighest point its velocity in the y direction is zero, so the velocity in the x direction is its total velocity...so now you have v0x...and they gave v0 so the formula v0x = v0 * cos(theta) will get you theta...i just figured this out now because i wanted to organize my messed up attempts for posting :P
     
    Last edited: Feb 5, 2005
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Hard projectile motion problem
  1. Projectile Motion HARD (Replies: 16)

Loading...