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Homework Help: Need help bulk modulus problem

  1. Feb 15, 2006 #1
    A solid ball of a special plastic material is to be used as a replacement joint for a patient’s hip. The mass per unit volume density of the ball is 900 kg/m3 and its radius is 1.5 cm. The ball is subjected to a test in which it is subjected to an increase in external pressure of 2 X 10 8 N/m2. The Bulk modulus of the ball is 2 X 10 9 N/m2.
    Assuming that the ball is compressed uniformly during this test, find the mass
    per unit volume density of the ball in its compressed state. The volume
    formula for a sphere of radius r is 4/3 pi r 3 .

    what Ive done so far:
    Volumem initial =1.414e-5

    change p= -B changeV/initial V

    change V=-1.414e-6

    mass of ball= 900 x 1.414e-5=.012735

    Im not really sure hwat to do next I tried to solve for density of the ball using the mass .012735 and the volume (change and then intitial) but both answers were wrong I know the answer is supposed to be 1000kg/m3 according to the book but im not getting that

    please help
  2. jcsd
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