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Is this the correct formula that im using for this question?

  1. Apr 15, 2007 #1
    1. The problem statement, all variables and given/known data
    hi this is the problem: the burning of the second stage of a two stage toy rocket takes the rocket from 12 m/s to 40 m/s in 5.0s. How far does the rocket during this time?

    2. Relevant equations
    would i use delta t= delta v/a ? would the given info be.. delta v1= 17 m/s, delta v2=40m/s and delta t=5.0s... if this isnt the correct formula please correct me. thank u all!:smile:
  2. jcsd
  3. Apr 15, 2007 #2
    distance = (1/2)*a*t^2 + vi*t

    where a = delta v / delta t

    and vi is the initial velocity (12 m/s)
  4. Apr 15, 2007 #3
    but the question asks for time
  5. Apr 15, 2007 #4


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    Staff Emeritus
    Science Advisor

    No it doesnt.. it asks for distance! Firstly, work out the acceleration using your equation, then plug this along with initial velocity and time into the equation for distance given in post #2.
  6. Apr 15, 2007 #5
    what do you mean by working out the acceleration?
  7. Apr 15, 2007 #6


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    Staff Emeritus
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    sorry, you'll just be going round in circles by doing that! you can use another of the "kinematic equations", namely [tex]d=\frac{v_i+v_f}{2}\cdot t[/tex].

    Here's a link to the kinematic equations http://www.glenbrook.k12.il.us/GBSSCI/PHYS/Class/1DKin/U1L6a.html. These equations are normally the tools you need for questions involving a constant acceleration.
  8. Apr 15, 2007 #7
    kk, thanks a bunch:tongue2:
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