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Urgent help needed on physics problem

  1. Sep 30, 2004 #1
    Urgent help needed on physics problem!!!

    A rocket is launched straight up with constant acceleration. Four seconds after liftoff, a bolt falls off the side of the rocket. The bolt hits the ground 6.40 s later.

    What is the rocket's acceleration?

    I have less than an hour to answer this online, please help.
  2. jcsd
  3. Sep 30, 2004 #2
    I have no idea how to relate the distances or anything. Any help in setting up equations would be great.
  4. Sep 30, 2004 #3
    Ok I made a little mistake before. R is the rocket's acceleration so the displacement for the first 4 seconds is d0 = 0.5 * R * 4^2 = 8R. The velocity it gains during this time is equal to R*T = 4R

    Now during the drop the displacement is given by d = d0 + v1*t + 0.5*(-g)*t^2

    At t = 6.4 seconds d and d0 are equal. Subbing in some stuff and knowing that d = 0 after 6.4 seconds 0 = 8R + 4R*6.4 - 4.9*6.4^2. Solve for R.
    Last edited by a moderator: Oct 1, 2004
  5. Sep 30, 2004 #4


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    5.95 m/s^2
  6. Sep 30, 2004 #5
    How did you get the answer tony?
  7. Sep 30, 2004 #6


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    I wrote a computer program, trying different values for a, until t = 10.4
    Code (Text):

    Private Sub Command1_Click()
    Dim a As Double, Vrocket As Double, Vbolt As Double, pRocket As Double, pBolt As Double
    Dim t As Double, sstep As Double

    sstep = 0.01
    pRocket = 0
    Vrocket = 0
    a = 5.95

    For t = 0 To 4 Step sstep
        Vrocket = Vrocket + a * sstep
        pRocket = pRocket + Vrocket
    Next t

    pBolt = pRocket
    Vbolt = Vrocket
    t = 4 + sstep

    While pBolt > 0
        Vbolt = Vbolt - 9.81 * sstep
        pBolt = pBolt + Vbolt
        t = t + sstep
    Text1.Text = t
    End Sub
  8. Sep 30, 2004 #7
    Sweet! Is that Visual Basic?
  9. Sep 30, 2004 #8


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    Yes, VB 6.0. That's how I do the problems I can't quite understand. It's called a numerical solution. There are some problems where no analytical solution exists, and a numerical solution is necessary.

    But I'm sure that an analytical solution exists for this problem, and I'm waiting to see if someone knows it. This is the type of problem I'm going to face in about 2 weeks. (And I'm not allowed to bring my laptop to tests :smile: )
  10. Oct 1, 2004 #9
    Read my post above sorry I posted an incorrect solution before it's about 5.96.
  11. Oct 1, 2004 #10
    thanks for the help guys.
  12. Oct 1, 2004 #11


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    Did you get it right? I imagine you're using an instant grading homework system?
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