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Basic algebra is not working

  1. Sep 9, 2012 #1
    Ok so here is my problem:

    Vf=Vi+at

    I want to solve for t so:

    (Vf-Vi)/a = t

    right so now my problem starts how can this happen:

    t = -Vf/a ??????

    The solution above comes from this site http://www.monmsci.net/~fasano/phys1/Chapter_2_10.pdf

    scroll down to problem 2.31 and you will find what I am looking at, in this situation Vi = 0 so they disregarded it and somehow during that process (at least i believe it was during that process) they came up with:

    t = -Vf/a

    Please explain to me how that works, where the heck did the - sign come from??
     
  2. jcsd
  3. Sep 9, 2012 #2

    jedishrfu

    Staff: Mentor

    looks like a typo to me. sometimes in gravity problems +v means its going up vs -v means its falling but thats not the case. notice in the actual answer the - is gone.
     
  4. Sep 9, 2012 #3
    Oh well I didn't even see that lol well thank you it prob. was just a typo
     
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