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Homework Help: Time for rocket shot upward to reach the ground

  1. Nov 14, 2008 #1
    1. The problem statement, all variables and given/known data
    A model rocket releases its first stage when it is 100.0 m above the ground and moving upward at 40.0 m/s. Ignoring air resistance, find:

    the time it takes the first stage to hit the ground
    2. Relevant equations
    Y=Yo+VyoT+1/2GT^2

    Quadratic

    3. The attempt at a solution

    I got to [-(40)+-Squareroot(1600-1960)]/9.8

    the problem is that the square root of a negative number is an imaginary number so I am just wondering what I am missing here?
     
  2. jcsd
  3. Nov 14, 2008 #2

    alphysicist

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    Homework Helper

    Hi helpmedude,

    I don't believe that is correct. What numbers did you use for Y, Y0, Vy0, and G?
     
  4. Nov 14, 2008 #3
    my bad I forgot to make acceleration due to gravity negative thats why it didnt work geez. thx anyways. Y=0 Yo=100m Vyo=40.0m/s G=-9.8m/s^2 I used 9.8m/s^2
     
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