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Homework Help: Determine the acceleration of the object during this motion

  1. Aug 31, 2008 #1
    1. The problem statement, all variables and given/known data

    An object moving on the x axis with a constant acceleration increases its x coordinate
    by 31 m in a time of 6.4 s and has a velocity
    of 20 m/s at the end of this time.
    Determine the acceleration of the object
    during this motion.

    2. Relevant equations

    3. The attempt at a solution
    What I did:
    found the initial velocity by dividing 31m/6.4s and got 4.84375
    used galileo's formula: V^2=Vi^2+2ax
    my answer was 6.3 or so and it was wrong

    I am not so sure that the initial velocity is right, but I cannot think of any ideas. Can someone assist me in the right direction?
  2. jcsd
  3. Aug 31, 2008 #2


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    Your instinct is correct. The increase in distance on the constantly accelerating object won't be given by simply dividing the 2.

    Rather don't you want to use the relationship that Vf = Vi + at?
  4. Aug 31, 2008 #3
    I'm assuming that LowlyPion is thinking the way that I am at the moment, so to add to his reply, I say:

    Since you don't know the initial velocity, use the relationship that he provided and substitute it into the equation:

    [tex]x = v_0t + \frac{1}{2}at^2[/tex]
  5. Aug 31, 2008 #4
    Ok, but the acceleration is also missing. Would I have to use one formula and substitute variables into another?
  6. Aug 31, 2008 #5


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    I think you are on to something. That would be the way to find a.
  7. Sep 1, 2008 #6
    We gave you the 2 that you should use.
  8. Sep 1, 2008 #7
    alright, i substituted the vf=vi+at into x=vit+1/2at^2
    and i got around .7

    right track?
  9. Sep 1, 2008 #8


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    I would suggest that you use the numbers of your problem, solving for unknowns along the way. It makes the algebra easier. (At least I find it so.)

    In looking at your work I think, without scratching it out myself, that looks on the right road.
    Last edited: Sep 1, 2008
  10. Sep 1, 2008 #9
    Look closely at what you left out at this stage.
  11. Sep 1, 2008 #10
    Ah yes, i forgot the t.

  12. Sep 1, 2008 #11
    Indeed that is correct.
  13. Sep 1, 2008 #12
    thanks a lot chislam and lowlypion
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