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Oopsy on a Test Problem - Acceleration

  1. Sep 20, 2005 #1
    I had a test question that went like this:

    Projectile is launched horizontally with an initial speed of 50 m/s. It started from rest, what is the acceleration after 3 seconds?

    For the life of me I couldn't come up with a velocity final or distance to find the acceleration, is there something I forgot that happens on Earth when a projectile is fired horizontally?

    Make sense, anyone?

    Thanks!
     
  2. jcsd
  3. Sep 20, 2005 #2
    well, assuming you are on earth, there is no air resistance and the projectile hasn't hit the ground yet, the acceleration is going to be 9.8m/s^2, because the only force acting on it is gravity.
     
  4. Sep 20, 2005 #3
    But isnt it only going horizontally? so the acceleration would be in the y direction, and this is x...
     
  5. Sep 20, 2005 #4

    eep

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    Were you given an initial height?
     
  6. Sep 20, 2005 #5

    HallsofIvy

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    Staff Emeritus
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    "But isnt it only going horizontally?"
    It was launched horizontally- it certainly won't keep going only horizontally!

    Assuming again that this was done on the surface of the earth, that you are ignoring air resistance and that the object has not yet hit the ground, the only acceleration (NOT velocity) is 9.81 m/s2 downward- there is NO horizontal acceleration.

    eep asked if you were given an initial height because of the possibility that the projectile would have already hit the ground- in which case there would be NO acceleration at all!
     
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