1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Stone Throw, Found answer but don't understand how ?

  1. Oct 4, 2009 #1

    Monocerotis

    User Avatar
    Gold Member

    1. The problem statement, all variables and given/known data
    A stone is thrown from a bridge with an initial vertical velocity of magnitude 4.0m/s/ Determine the stone's velocity after 2.2s if the direction of the initial velocity is (a) upward, and (b) downward. Neglect air resistance.


    2. Relevant equations
    Aav=Vf - Vi / Δt

    Vi + Aav(Δt) = Vf

    3. The attempt at a solution

    b) 2.6 x 101m/s
    Easy to find as you enter in the given information into the formula.

    (a) on the other hand I have difficulty understanding. I attempted the problem, with this formula
    (-Vi) + Aav(Δt) = Vf. The answer I got corresponds to the answer in text, but I don't really understand how that works. I'd like to know for similar problems in the future.
     
  2. jcsd
  3. Oct 4, 2009 #2
    You use the same equation to solve both problems, but if v_i is positive in b, it must be negative in problem a.
     
  4. Oct 4, 2009 #3

    Monocerotis

    User Avatar
    Gold Member

    Yes that's apparently obvious, I want to understand why however. The "theory" behind it.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook