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Impulse graph question

  1. Jun 6, 2012 #1
    1. The problem statement, all variables and given/known data



    2. Relevant equations
    fnet(delta t) = m (delta v)


    3. The attempt at a solution
    I need some help on question b ASAP (i'm not sure what the question means when it says find the velocity AT THE END of the 1.20 sec impact)
    and i would like for someone to check if i've answered question A correctly
     

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  3. Jun 6, 2012 #2
    A looks right.


    And for part B, the problem seems set up where that graph of F vs. t is the forces acting on the player for 1.2s. It gives you an initial velocity, and asks what those forces (so the impulse that you already calculated) make her final velocity.
     
  4. Jun 6, 2012 #3

    SammyS

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    attachment.php?attachmentid=48101&d=1339036908.png

    What does the Impulse - Momentum Theorem say ?
     
  5. Jun 7, 2012 #4
    not sure
     
  6. Jun 7, 2012 #5
    The impulse is defined as the integral of a force with respect to time. Wiki "impulse" if you need more help
     
  7. Jun 7, 2012 #6

    SammyS

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    Momentum Theorem is something like:

    An object's change in momentum is equal to the net impulse on the object.


    Look it up to be sure!
     
  8. Jun 7, 2012 #7
    i believe i've found the integral in part A but i don't know what part b means by "find the velocity at 1.20 seconds"

    i've got the following information compiled for part b)
    fnet(delta t) = m (delta v)
    delta t = 1.20 seconds
    Fnet = ?
    m = 60 kg
    vi = 7.0 m/s
    vf = ?

    my problem is that i don't know what fnet is.
     
  9. Jun 7, 2012 #8
    I=Δp

    so you know your initial momentum. Now find the final momentum, using the above fact. :biggrin:
     
  10. Jun 7, 2012 #9
    What's the name for fnet(delta t)?
     
  11. Jun 7, 2012 #10
    impulse. however, i don't know if i did part A right and i don't know if they want me to use all the information in question B... and i do not understand what they mean by AFTER 1.20 seconds
     
  12. Jun 7, 2012 #11

    SammyS

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    Look at the graph again .
     
  13. Jun 7, 2012 #12
    You have an initial momentum - think about how that impulse ( change in momentum) will change the player's speed. (you're looking for pf)
     
  14. Jun 7, 2012 #13
    Your part A was right.

    And it just means that at t = 0 the velocity is 7, what is the velocity at t = 1.2?
     
  15. Jun 7, 2012 #14
    i think i got it
    -360 n*s = 60(vf-7)
    -6=vf-7
    vf=1 m/s
    ?
     
  16. Jun 7, 2012 #15
    correct
     
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