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!

Projectile Motion marble Problem

  1. Sep 24, 2009 #1
    1. The problem statement, all variables and given/known data
    A marble rolls off a table with a velocity of 1.93 m/s [horiz]. The tabletop is 76.5 cm above the floor. If air resistance is negligible, determine the velocity at impact.
    -[tex]\Delta[/tex]t has been found in a previous question; =0.395 s
    -I know the answer is 4.33 m/s [63.5 degrees below the horizontal]
    2. Relevant equations
    [tex]\Delta[/tex]d=-.5a([tex]\Delta[/tex]t)2-v2([tex]\Delta[/tex]t)


    3. The attempt at a solution
    [tex]\Delta[/tex]d=-.5a([tex]\Delta[/tex]t)2-v2([tex]\Delta[/tex]t)
    0.765 = -.5(9.8)(.395)+v2(.395)
    but I get velocity to equal 1. something m/s?
     
  2. jcsd
  3. Sep 24, 2009 #2
    Do you want to exclusively use kinematics, or do you just want the answer? If you just want the answer, I say go the easy route: energy. I've said this before on this forum already.

    Be sure to only consider the y-axis energy.
     
  4. Sep 24, 2009 #3
    i have to do it the kinematics way..
    don't confuse me with the energy just yet! haha.
     
  5. Sep 24, 2009 #4
    Using kinematics makes it more confusing actually. =)

    But to answer your question, if you know the time it takes to fall, and you know what acceleration it goes through, it's a simple matter of [tex]v_f(t) = v_0 + a t[/tex]. Plug in initial velocity in y direction and time, then you have the y component of the velocity vector. Air resistance is nonexistent, so the horizontal velocity stays the same. Take the magnitude of this vector.

    I plugged in the numbers myself (using WolframAlpha!) and got the right answer.
     
  6. Sep 24, 2009 #5
    V2 is not final velocity, it's initial velocity and in the y direction it is equal to?
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Projectile Motion marble Problem
Loading...