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Homework Help: Momentum, Gravity and Friction Mixed Problem

  1. Jan 28, 2008 #1
    1. The problem statement, all variables and given/known data

    A 15g bullet is fired from a gun, leaving the gun with a muzzle velocity of 750m/s. It hits and sticks in a 1250g wooden block. The block is on a table 5.0m away from edge. The table is 1.1m above the floor and between the block and the table surface constant of kinetic friction is 0.50. Will the block slide off the table and if so what will be the horizontal distance from the block to the table base when the block hits the floor?

    2. Relevant equations

    Momentum equation , dynamics, friction and Fg

    3. The attempt at a solution

    so basically we find the intial velocity of wooden block with the help of given data of bullet b/c momentum has been conserved. so block is moving. or maybe m wrong. this question has confused me. suppose the block is moving then how do we know how far it will go. I have some idea but how do i derive equations and find the answer,
    Plzz help. Its very important.
  2. jcsd
  3. Jan 28, 2008 #2
    use conservation of momentum.
    after the bullet sticks it has the same velocity as the block and hence it is a inelastic collision.
    calculate final velocity of block and bullet.

    That becomes the initial velocity for the block.

    Now see if the mass*accln of block is greater than frictional force or not.
    if yes.....then:
    Use force equation to calculate accln of block.

    Now calculate its velocity after it reaches the edge of the table i.e. travels 5m.

    Then take the block to be a projectile to be fired horizontally and calculate the range.

    HERE take vertical height as height of table i.e. 1.1m
  4. Jan 28, 2008 #3
    i have no delta(t) here?
    how i u suppose to sub it in equation?
  5. Jan 28, 2008 #4
    i think i got it, using kinematics eqs.
    but if u wanna explain it to me to clarify then it would be very nice. thanks. :D
  6. Jan 29, 2008 #5
    sure frnd but first show me ur work how u r proceeding...
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