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Verticle height. Please help

  1. Oct 20, 2007 #1
    Verticle height. Please help!!!

    A 12.0 g rifle bullet is fired with a speed of 360 m/s into a ballistic pendulum with mass 6.00 kg, suspended from a cord 70.0 cm long.

    Compute the vertical height through which the pendulum rises in cm.

    How would you find the verticle height? I have the equation KE=(sum of the masses)(gravity)(h) to find it but I get 13.23 and thats not right. I found the initial kenitic energy of the bullet to be 778J and the kinetic energy of the bullet and pendulum immediately after the bullet becomes embedded in the pendulum to be 1.55J.

    Can someone please help me?
  2. jcsd
  3. Oct 20, 2007 #2
    KE of the bullet & block as 1.55 J is correct. Re calculate equating this KE with increase in potential energy (mgh) to get the vertical height h. It wont be 13.23 cm
  4. Oct 21, 2007 #3
    Thank you soo much! I got it. I thought you had to have the KE as 1.55J +778J on the left hand side of the equation. Thats why i was getting it wrong. But thank you!!
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