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SoLid Pressure on this case

  1. Apr 4, 2005 #1
    Ok guys everyone knows teh solid Pressure = P / S but i have a question..
    I though about an object that falls from 20 meters.(Its mass is 2 kg, 2x2x2 meters cube)
    When it reaches the ground how much pressure does it make , in normal case
    20 . 10 / 2² = 50 Pascal it makes.However how can I calculate the pressure made by a falling object that has a downwards velocity ?

    THankkss , that can be a foolish question but I couldnt understand this.
  2. jcsd
  3. Apr 4, 2005 #2

    Andrew Mason

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    It depends on how long it takes to stop. It is just a mechanics question involving change of momentum.


    [tex]F = mg + mv/\Delta t[/tex] (assuming constant stopping force)

    [tex]P = F/A = \frac{mg + mv/\Delta t}{A}[/tex]

    Last edited: Apr 4, 2005
  4. Apr 4, 2005 #3
    Thanks that is a very logical thought , and probably the correct one I had never thought this :) I will Try :=)
  5. Apr 4, 2005 #4
    Those equations are alittle messed up andrew, they say that the force decreses the faster you stop :)

    It should be:

    [tex]F = mg + \frac{mv}{\Delta t}[/tex]

    [tex]P = F/A = \frac{mg + \frac{mv}{\Delta t}}{A}[/tex]

    v is the velocity at the time of impact, which you can find from kinematics.

    For the record, this equation assumes no bouncing.
  6. Apr 4, 2005 #5

    Andrew Mason

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    Right you are! [itex]F\Delta t = mv [/itex]

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