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Dynamics rocket car problem

  1. Feb 17, 2013 #1
    1. The problem statement, all variables and given/known data

    A 1200 kg rocket car is placed at the bottom of a 100 meter long ramp inclined at 10°. The rocket is turned on and it exerts a force of 8300 N for 5.70 seconds, and then it shuts down. Find the speed with which the rocket car leaves the ramp (assume frictionless).


    2. Relevant equations

    http://img98.imageshack.us/img98/9425/54fl1.png [Broken]

    3. The attempt at a solution

    http://i.imgur.com/MGDp7Rf.png?1

    I didn't show all of my solution but I need to know if that part is correct. What I did next is I assumed vi = 0 and the used the formula vf = vi + at which gave me an answer of 29.7 m/s, however, the correct answer is 28.8 m/s.
     
    Last edited by a moderator: May 6, 2017
  2. jcsd
  3. Feb 17, 2013 #2

    haruspex

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    You've calculated the max speed. Did you use the ramp length?
     
  4. Feb 17, 2013 #3
    What do I do with the ramp length? I didn't use it.
     
  5. Feb 17, 2013 #4

    haruspex

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    You're asked for the speed at the end of the ramp, not the speed when the engine shuts down.
     
  6. Feb 17, 2013 #5
    So would I calculate the distance traveled up to when the engine shuts down, then subtract it from the length of the ramp to find the remaining distance?
     
  7. Feb 17, 2013 #6

    haruspex

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    That'll work.
     
  8. Feb 17, 2013 #7
    I'm not sure how to get the new acceleration from when the engine shuts down. I know that it has to be negative because the rocket will slow down.
     
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