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Urgent question: G-Force, Deceleration, loads

  1. May 10, 2008 #1
    Hello...

    If an object weighs 4500kg and travels @ 5kph (138cm/s) then stops in 15cm:

    what is Gforce?

    Decceleration?

    Also, if object was stopped via a collision and if contact face is 100cmx15cm then what is impact force kg/sq.cm?

    This information is really important to me for a professional argument that may save my job so ANY help/resources would be immensely appreciated.

    Yes I did have an accident at work... :redface:

    My only defence is going to have to be with cold science.

    At 36, my algebra has rusted through as this is the first time i've had to find "x" so really need some whizzy help.

    Thanks to anyone kind enough to help.

    David
     
    Last edited: May 10, 2008
  2. jcsd
  3. May 10, 2008 #2
    If something travels with the initial velocity V.......
    1.38m/s

    and then stops over the distance L,.....................
    0.15m

    then, assuming constant decelleration,

    L = V^2/2a...........................................

    0.15m=1.38m^2/2 x 6.348
    0.15=1.9044/12.696


    where V - initial velocity
    a - absolute value of decceleration.
    V^2 means "V squared"

    From this, you can find

    a = V^2/2L................................................ ......

    a=1.38m^2/0.30m
    a=6.348m/s

    From the Newton's law,

    a = F/M................................................. ...

    6.348m/s=28566n/4500kg

    where F is the force that acted during the slowdown and M is the mass.

    We then have

    F = MV^2/2L.............................

    4500kg x 1.38m/s^2 /2 x 0.15m
    4500 x 1.9044 / 0.30m
    8569.8/0.30
    F=28566n

    Use M in kilograms, V in meters per second and L in meters. You'll get the force in Newtons.

    I don't know what is Gforce.

    Then the pressure is by definition the force divided by area. Diveide the force you've obtained by the area and you'll get pressure in Newtons per unit of area (whatever units you use).....

    28566n/1.5m=19044n/sq m
    or 1941.9kg/sq m

    If someone could check this please I'd be grateful as i'm a little woozy with painkillers.

    Thank you so very much.
     
  4. May 10, 2008 #3

    alphysicist

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    Homework Helper

    Hi exalto1,

    I'm not sure about these numbers. The area in square meters is .15 m^2.

    G-force is usually the acceleration measured in units of g=9.8 m/s^2.
     
  5. May 11, 2008 #4
    Hello alphysicist...

    Are these figures better:


    P = 28566N/1500cm^2=19.044N/cm^2 or
    P =~1.94kg/cm^2 or
    P=~19400kg/m^2
     
  6. May 11, 2008 #5

    alphysicist

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    Homework Helper

    Your math look okay to me, if those are the units you want. Using kg/cm^2 for the pressure reminded me that a unit that some people use for force is the gram-force. I would think that's probably what they meant by Gforce, so your choice of mass/area as the units for pressure would be what they wanted.
     
  7. May 11, 2008 #6
    Thank you so very much Al
     
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