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Predicting Time of Flight

  1. Nov 2, 2011 #1
    1. The problem statement, all variables and given/known data
    A system is setup to launch an object horizontally off desks with an initial speed of 4.2 m/s. Height of desk is 1.3 meters.

    What time of flight should be predicted for the object?

    2. Relevant equations
    Δt = (v2 - v1) / ∂ (Not too sure)

    3. The attempt at a solution
    1.3/4.2 = 0.31 seconds

    Hello. I tried to find the time, but I keep getting the time wrong. The actual answer is 0.52s, but I think I'm going the wrong way about it :( Can someone help me understand the question more and lead me into the right direction? I'm not very good at physics.
  2. jcsd
  3. Nov 2, 2011 #2
    Are you aware of the X and Y table method?

    Make an X and Y table
    Like this


    In the X column, put all of your X axis information (you have velocity)

    And in the Y column put down all of your Y axis information (you always have acceleration due to gravity, you have height/distance in this question as well)

    Now, remember that for horizontal you always use d = tv, and for vertical it's always d = vit + 1/2at^2.

    Use those formulae with the information you have in the respective columns to find the unknown variables.

    Time will be equal in both columns, it is the only factor that does not change because it's neither an X nor a Y nor a Z vector, so if you get time in one column you will effectively have time in both columns.
    Last edited: Nov 2, 2011
  4. Nov 2, 2011 #3
    Ohh..! Thank you so much! You saved me!
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