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Kinematics problem: Ball rolling off ramp & table

  1. Apr 25, 2016 #1
    1. The problem statement, all variables and given/known data
    http://imgur.com/0t8TVgq
    http://imgur.com/0t8TVgq
    upload_2016-4-25_17-2-26.png
    [Image copy inserted by moderator]
    Sorry about all the erase marks. My question is why is the final velocity not 0.

    2. Relevant equations
    V=Vo+at




    3. The attempt at a solution
    So the question is asking for the horizontal distance the ball travels before it hits the floor. First to solve this I decided to solve for time. To do this is used V=Vo+ at which I rearranged to t=(V-Vo)/a. Using just the vertical component, I decided the vertical velocity of the ball when it reaches the floor is 0. So I did (0-1)/-9.8 which gave me a time of .102. The book solved for the final distance first and then solved for time
    My question is why is the final velocity no just 0. When it reaches the floor it can't have a positive velocity because it has stopped moving.
     
  2. jcsd
  3. Apr 25, 2016 #2

    SteamKing

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    You know the ball falls for a certain distance when it rolls off the table. There's a SUVAT equation which deals with distance traveled under uniform acceleration, given an initial velocity. Why didn't you use this equation to find the time of the fall?
     
  4. Apr 25, 2016 #3

    haruspex

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    No, that is after it has hit the floor. The equation you used is only valid for constant acceleration, so only until it is just about to touch the floor.
     
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