1. Limited time only! Sign up for a free 30min personal 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!

Finding Time For Projectile Motion

  1. Dec 15, 2011 #1
    1. The problem statement, all variables and given/known data

    A marble launcher shoots a marble with a launch velocity of 6.89 m/s @15.0 degrees above horizontal.

    -Find the marble's range.



    (I tried to do this but I need to be able to find the time for horizontal motion... how would I do that?)

    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
  3. Dec 15, 2011 #2

    PeterO

    User Avatar
    Homework Helper

    The time is calculated by considering the vertical component of the motion, and treating it like any other vertical motion example.

    Or you could have a read of the

    http://en.wikipedia.org/wiki/Range_of_a_projectile

    then you only need a substitution - provided your projectile is landing at the same level it was launched from and not from/onto a hill/cliff/building.
     
  4. Dec 16, 2011 #3
    Because its 6.89m/s @ 15.0deg, you can use trigonometric functions to find the initial vertical and horizontal speed:

    vertical:
    sin(15.0) = o / 6.89

    horizontal:
    cos(15.0) = a / 6.89

    Since the horizontal velocity is constant as gravity does not affect it, the time the projectile is in the air can be found by:

    v = a*t

    where

    v = vertical
    a = acceleration due to gravity
    t = time of projectile

    Once you have the time of the projectile its simple.

    We know that distance = velocity * time

    -> d = v * t

    where d is the "range" we are trying to solve for
    where v is the HORIZONTAL velocity
    where t is the time of the projectile


    Once you have done this, post your work/solution so I can help you further. Nobody here is going to do you homework for you, we can only HELP you if you are trying.
     
  5. Dec 17, 2011 #4
    jack343, you are forgetting that the projectile goes up AND down so the time of flight is double what you calculate.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook