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Homework Help: Momentum question

  1. Jul 24, 2006 #1
    A rifle bullet of mass .01kg strickes and embeds itself in a block of mass .99kg which rests on a horizontal frictionless surface and is attached to a coil spring.The impact compresses the spring 10cm. Calibration of the spring shows that a force of 1.0N is required to compress the spring 1cm. (a) find the maximum potential energy of the spring. (b) find the velocity of the block just after the impact.(c) What was the initial velocity of the bullet?
    My solutions: m1=.01kg, m2=.99kg: F=-kr; => k= F/r = 100N/m
    (a)P.E. = .5kr^2 = 0.5 Joules.
    (b).5m2xv2^2 = .5J => v2= 1 m/s
    (c)m1v1=(m1+m2)v2 => v1=1/.01 = 100 m/s.
    That velocity is too low for a bullet, I must be doing something wrong.
  2. jcsd
  3. Jul 24, 2006 #2
    Must be a very old design. ;)
  4. Jul 24, 2006 #3
    Apparently, you did all correct. I have just done (a), (b), (c) and came up with the same results. :smile:

    neutrino must be right. :biggrin:
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