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Homework Help: Two Stage Rocket

  1. Jan 23, 2013 #1
    1. The problem statement, all variables and given/known data

    In the first stage of a two-stage rocket, the rocket is fired from the launch pad starting from rest but with a constant acceleration of 3.50 m/s^2 upward. At 25.0 seconds after launch, the second stage fires for 10 seconds, which boosts the rocket's velocity to 132.5m/s upward at 35 seconds after launch. This firing uses up all the fuel, however, so after the second stage has finished firing, the only force acting on the rocket is gravity. Air resistance is negligible.

    A) Find the maximum height that the stage two rocket reaches above the launch pad.

    2. Relevant equations

    y=yo + vo*t +1/2*a*t^(2)

    vy=vo + a*t

    3. The attempt at a solution

    First stage:
    y=yo + vo*t +1/2*a*t^(2)

    Vy=Vo + a*t
    Vy=3.50m/s^(2)*25s= 87.5m/s
    Final velocity of first stage=87.5m/s

    Second Stage:
    Initial velocity of second stage=87.5m/s
    132.5m/s=87.5m/s +a*10sec

    New acceleration=4.5m/s^(2)

    y=yo + vo*t +1/2*a*t^(2)

    y=1093.75m + 87.5m/s*10s + 1/2(4.5m/s^(2))*100s= 2193.75m

    Is this the correct answer? Thanks!
  2. jcsd
  3. Jan 23, 2013 #2


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    Science Advisor
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    Gold Member

    Yes, it looks right. It would have been slightly simpler to compute the stage two height delta by average velocity: 2s = (v0+vf)t
    I assume there are more parts to the question.
  4. Jan 23, 2013 #3
    Thanks and yes there are more parts to this question. I am going to work on them and then post them back on here.
  5. Jan 24, 2013 #4


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    2017 Award

    Staff: Mentor

    2193.75m is the height after the second stage finished firing - but the rocket still has a velocity upwards, and will continue to increase its height afterwards.
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