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Homework Help: Questions dealing with force

  1. Sep 14, 2005 #1
    A couple of questions in this problem.

    A 20,000kg rocket has a rocket motor that generates [tex]3.0 *10^5N[/tex] of thrust.

    1. What is the rocket's initial upward acceleration?

    I used the formula F=MA and got 15 but apparently thats not the right answer. So Im stumped.

    2. At an altitude of 5000m the rocket's acceleration has increased to 6.0m/s^2. What mass of fuel has it burned?

    Im assuming I need the answer to the first part and that the 5000m is irrelevant.

    [tex]300000=m_1*6[/tex] Then I should be able to get the answer [tex]20000-m_1[/tex]

  2. jcsd
  3. Sep 15, 2005 #2
    I think you are on the right track. With problems like these the first step is to draw a free body diagram then sum the forces - perhaps the problem states that the rocket is taking off from Earth? After summing the forces you should have the answer for the Total a. Let me know if that helps.

  4. Sep 15, 2005 #3
    Ah ok I see why my answer is wrong. I needed to subtract weight from the thrust.
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