1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Inelastic Collision with Friction

  1. Oct 16, 2004 #1
    I forget how to solve one dimensional motion problems with friction, which is holding me up in this problem:

    a 5.00 g bullet is fired horizontally into a 1.2 kg wooden block resting on a horizontal surface. The coefficient of kinetic friction between the block and surface is .2. The bullet remains embedded in the block and the block moves 0.23 m before stopping. What is the initial speed of the bullet?



    bullet------->block----.230 M-[ ]

    looking at it as a momentum problem:

    M(bullet)*V(bullet) = M(Bullet+Block)*V(bullet+block)

    you need to solve for v(bullet+block) which can be determined by the following problem:

    A block of mass 1.25 kg on a surface with kinetic friction of .2 is acted on upon a force and move .230 M before coming to rest on a horizontal surface. Find the initial speed of the bullet.


    m = 1.25
    v_0 = x
    v_x = 0
    mu_k = .2
     
  2. jcsd
  3. Oct 16, 2004 #2

    arildno

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    Dearly Missed

    Well, in the second phase, you have constant deceleration equal to 0.2g
     
  4. Oct 16, 2004 #3
    I understand that.

    What I dont understand is the logic to find the initial velocity.

    I know what this answer is, but I need to apply the exact same logic to a seperate problem. So what I am really asking for is someone to solve this problem and show the steps.

    Gallium
     
  5. Oct 16, 2004 #4

    arildno

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    Dearly Missed

    Well, you have:
    [tex]v_{f}^{2}-v_{0}^{2}=2*(-0.2g)d[/tex]
    Right?
    ([tex]v_{f}=0[/tex], d is 0.230)
    This enables you to solve for [tex]v_{0}[/tex]
     
  6. Oct 16, 2004 #5
    that doesnt yield the correct answer.
     
  7. Oct 16, 2004 #6

    Pyrrhus

    User Avatar
    Homework Helper

    Because that's the speed for the bullet+box system, not for the bullet, now use conservation of momentum to find the initial speed of the bullet.
     
  8. Oct 16, 2004 #7
    .05 * V_1 = .9212*1.25

    V_1 = 23.03 m/s

    V_1 actually = 229 m/s
     
  9. Oct 16, 2004 #8

    Pyrrhus

    User Avatar
    Homework Helper

    1 Kg is 1000 grams not 100 grams.

    5grams is 0.005 Kg.
     
  10. Oct 16, 2004 #9
    i see, thank you. I found the correct logic.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Inelastic Collision with Friction
Loading...