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Homework Help: Newtons 2nd Law

  1. Jan 28, 2008 #1
    1. The problem statement, all variables and given/known data
    Ok this is kind of long. This is the 4th question on my homework assignment and I need to give background on the first 3 to make sure I got those correct.
    1. I am sure on this since it was simply finding the weight of a rocket ship that has an intial mass of 3kg. Answer is 30N

    2. Question is: Let's assume half the mass of the rocket is fuel and is spewed out nearly instantaneously. If the fuel for the rocket travels downward at a velocity of 40 m/s then what will be the initial velocity of the rest of the rocket? My answer is 40m/s Is this correct?

    3. Instead of saying it is instantaneous lets say that the fuel was ejected in a time of 0.2 seconds.
    A. Ignoring gravity during this time, what is the acceleration on the rocket during this time. I used A=change in Vel/Time and got 200 m/s
    B. What is the force on the rocket during this time? I used F=MA and got 300N Up

    Ok, IF these are all correct here is the question that I cannot figure out.

    4. Near the ground there is no wind
    A. What is the velocity of the rocket in the East Direction?
    B. What is the velocity in the up direction?

    2. Relevant equations

    3. The attempt at a solution

    I know velocity=change in position/time but not real sure what #'s to use here and really it doesn't make alot of sense to me. Do I need to use 10m/s for gravity in here somewhere?
    Thanks for any help.
    Last edited: Jan 28, 2008
  2. jcsd
  3. Jan 28, 2008 #2

    Shooting Star

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    Your answers to 1, 2 and 3 are correct.

    4-A. Zero, because there is no horizontal force.
    4-B. Doesn't make sense if you ignore gravity. It'll be still 40 m/s.
  4. Jan 28, 2008 #3
    Thanks. So if we weren't ignoring gravity would it be 10m/s?
  5. Jan 28, 2008 #4

    Shooting Star

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    How do you arrive at this value?
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