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Finding the speed of a bullet via device with two rotating disks

  1. Oct 17, 2011 #1
    1. The problem statement, all variables and given/known data
    The device consists of two rotating disks, seperated by a distance of d = 0.879 m, and rotating with an angular speed of 96.1 rad/s. The bullet first passes through the left disk and then through the right disk. It is found that the angular displacement between the two bullet holes is θ = 0.161 rad. From these data, determine the speed of the bullet.

    Basically, I'm lost in this equation.
  2. jcsd
  3. Oct 17, 2011 #2
    What do you mean left disk, then right disk? How are the disks arranged? Are they both turning on the same shaft one behind the other? A sketch would be informative. Also, please show what equations you are working with.
  4. Oct 17, 2011 #3
    θ=s/r & w=Δθ/Δt & α=Δω/Δt

    Attached Files:

  5. Oct 18, 2011 #4
    OK, let's get started thinking about this problem.

    What do you know about distance, time, and speed? How are they related mathematically?

    You know how fast the disks are turning and therefore know how long it takes to make one complete revolution. You know how much the disks turned between bullet holes. You know the distance between the disks.

    This data can be related to determine the speed of the bullet. Let's see how you put it all together to solve the problem.
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