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Homework Help: Pressure~gas law

  1. Jun 23, 2013 #1
    1. The problem statement, all variables and given/known data
    rain is falling normally on a circular region of radius 25cm at a rate of 1.2gs-1
    suppose the velocity of each raindrop just before it reaches the region is 10cms-1
    and the collision between each raindrop and the region is perfectly elastic
    find the avg pressure exerted on the region

    take g=9.8ms-1

    2. Relevant equations

    P= F/A

    3. The attempt at a solution

    momentum, then the Pressure
    is it ...P = (0.0012X10+0.0012X9.8) / 0.25^2 pi??
  2. jcsd
  3. Jun 23, 2013 #2

    Andrew Mason

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    If the collisions are perfectly elastic, what is the change in momentum of a raindrop of mass m striking this area?

    Now take N such raindrops every second such that Nm = 1.2 g. What is the total change in momentum of the raindrops every second? How is that change in momentum every second related to the force imparted to the circular area? What is that force/unit area?

  4. Jun 23, 2013 #3
    can i take t=1
    then mv-mu/t = F can be count
    then mass = 1.2 X 1
    then Pressure (P) can be count
  5. Jun 23, 2013 #4


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    If you use the units and parentheses properly, the method will work. What is u if the collision is perfectly elastic?

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