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Velocity of an object dropped

  1. May 1, 2013 #1
    1. The problem statement, all variables and given/known data

    What is the velocity of an object dropped from a height of 300 m when it hits the ground?


    2. Relevant equations

    s(t) = s0 +v0t -1/2gt2

    v(t) = v0 - gt

    s0 = initial height

    v0 = initial velocity

    v(t) = s'(t)

    3. The attempt at a solution

    Attempted this for a while, can't seem to get it right. I know initial height = s0 = 300m.

    g, as given by the book = 9.8 (represents gravity)

    I understand that when trying to find maximum height, velocity = zero. For this, I assume maximum velocity is found when s(t) = zero. Should I believe that when s0 = 300, v0 and t = zero?
     
  2. jcsd
  3. May 1, 2013 #2
    Remember that g is -9.81 m/s2. That is, it is a negative value.
    try this equation:


    v2 = v02 + 2g(x-x0)
     
  4. May 1, 2013 #3
    I appreciate you giving me a new equation, but I'm trying to solve this within the context of the information given. I doubt I'm supposed to solve using that equation. No offense intended.
     
  5. May 1, 2013 #4
    From the given eqn.s
    you can use s(t) = s0 +v0t -1/2gt2
    put s0 =0;v0t=0;g=9.8m/s2;s(t)=300m

    from this you will get time(t) required for the body to reach the ground.

    now take the equation

    v(t) = v0 - gt

    put v0 =0;g=9.8m/s2
    also put the time(t) found from the previous eqn.

    v(t) is the required velocity.
     
  6. May 1, 2013 #5
    Dammit. Thanks nil. Dammit dammit..I was so close. I just had a few things wrong here and there..

    But yeah, I had the right idea, was so close. Oh well.
     
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