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Math Help - Momentum and Velocity

  1. #1
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    Momentum and Velocity

    hey, im new to the forum, im having a lot of trouble with my last engineering assignment,
    If someone could point me in the right direction much applyed
    Btw its a mechanical principles question.

    Question: A nail gun of a mass of 2kg fires 20g nails; it experiences a retarding force of 50N and recoils by 1.25cm after each nail is fired. Find the initial speed of the nail leaving the gun.

    So at the moment what i have worked out is...
    Momentum before = momentum after
    Mgn Vgn = Mg Vg + Mn Vn
    Momentum before is 0 as nothing as nail hasnt been fired

    To find V im using V2 = u2 + 2as (the first 2's are ment to be powers)
    when s= displacement (i gaver this is recoil? so it would be 1.25cm)
    u = inital velocity
    v = final velocity
    a = acceleration (A=F/M=50/0.02= 2500m/s)
    t = time

    Rep will be given, i need this assignment done for monday so i can stay on the college course im doing
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  2. #2
    Super Member malaygoel's Avatar
    Joined
    May 2006
    From
    India
    Posts
    648
    You have figured out

    m_{gun}*u_{gun}=m_{nail}*u_{nail}

    only u_{gun} is troubling you.

    you have taken the correct steps

    To find V im using V2 = u2 + 2as (the first 2's are ment to be powers)
    when s= displacement (i gaver this is recoil? so it would be 1.25cm)
    u = inital velocity
    v = final velocity=0
    a = acceleration (A=F/M=50/0.02= 2500m/s)
    t = time
    only this is that since this is retardation, a=-\frac{F}{m_{gun}}=-25

    v^2-u^2=2as

    giving
    u(=u_{gun})=\sqrt{2*25*.0125}
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