Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Forensic Expert Bullet Velocity-Ballistic Pendulum :uhh:

  1. Nov 2, 2006 #1
    A forensic expert needed to find the velocity of a bullet fired from a gun inorder to predict the trajectory of a bullet. He fired a 5.50g bullet into ballistic pendulum with a bob that had a mass 1.75 kg. The pendulum swung to a height of 12.5 cm above its rest position before dropping back down. What was the velocity of the bullet just before it hit and became embedded in the pendulum bob?
    :cry:

    I think I have an understanding of the queation, but just wanted to ensure I am on the right path.

    I figured that in the middle kenetic energy E=1/2 mv2 will not be conseved, but momentum is conserved. So if u is the velocity of bullet in start then u=((m+M)v)/m

    In the swing to the height of 12.5 cm the potential and kenetic energy will be conserved since both the mass of pendulum and bullet swing up after collision.
    so v=sqrt(2gh)

    v=sqrt(2*9.8*0.125)
    =1.565 m/s

    u=((m+M)v)/m
    =((5.50+1750)1.565)/5.50
    =499.599 m/s

    Is this question really this easy because its 4 marks?

    Please help. Thank you. :confused:
     
  2. jcsd
  3. Nov 2, 2006 #2

    OlderDan

    User Avatar
    Science Advisor
    Homework Helper

    Yes it is.
     
  4. Nov 2, 2006 #3
    Thanks a lot!
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook