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Homework Help: Rocket Science? perhaps

  1. Oct 17, 2012 #1
    1. The problem statement, all variables and given/known data

    A 2.45×10^4-kg rocket blasts off vertically from the earth's surface with a constant acceleration. During the motion considered in the problem, assume that remains constant. Inside the rocket, a 13.1-N instrument hangs from a wire that can support a maximum tension of 33.9N .

    Find the minimum time for this rocket to reach the sound barrier (330m/s) without breaking the inside wire.

    Find the maximum vertical thrust of the rocket engines under these conditions.

    How far is the rocket above the earth's surface when it breaks the sound barrier?

    2. Relevant equations

    F = ma
    w = ma
    vx = v0x + axt

    probably missing a couple

    3. The attempt at a solution

    The only thing I could think to do so far is to calculate the downward force acting on the rocket which would be weight?

    so 24500 x 9.8 = 240100N acting downward

    I don't know how to find the upward force.
    I don't know what all this hanging instrument stuff is?

    Help is much appreciated! Thanks c:
  2. jcsd
  3. Oct 17, 2012 #2
    well so imagine you're dragging some object along a frictionless surface (say, ice) and you're pulling it with a rope

    let's say you can accelerate at will (like you've got a jetpack on or something)

    so when you're pulling this object along, it will experience a force, yeah?

    Same idea here. The hanging instrument is being pulled upwards by the same force that is pushing the rocket up into the air.
  4. Oct 17, 2012 #3
    so the string can handle 2.587 times the force it's handling right now right? but how do I incorporate that into an equation to find speed or acceleration?
  5. Oct 17, 2012 #4
    the string can support 33.9N, and is feeling 13.1N when the system is at rest. How much more force can be applied before it breaks?
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