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: Help with a question

  1. Sep 24, 2006 #1
    8. A karate master strikes a board with an initial velocity of 10 m/s, decreasing to 1 m/s as his hand passes through the board. If the time of contact with the board is 0.002 s, and the mass of the coordinated hand and arm is 1 kg, what is the force exerted on the board.

    a. 1000 N
    b. 1800 N
    c. 2700 N
    d. 4500 N

    - well, I lost my book cuz my backpack got stolen and I have an older physics book i got from a freind and the pages dont match up with my study guide. I cant find the right equation for this. I need an equation that uses change in velocity, contact time, and mass of the object to get F in Newtons. If anyone can show me how I do this or at least point me in the right direction I would appreciate it.
     
  2. jcsd
  3. Sep 24, 2006 #2
    Momentum=Impulse

    mv=Ft
     
  4. Sep 24, 2006 #3
    so...

    m = mass
    v= change in velocity?
    F= force in N
    t= time

    is v the initial, final, or change in velocity?

    if it is change in velocity, then i get:

    9*1/0.002 = 4500 N

    Is this right?
     
    Last edited: Sep 24, 2006
  5. Sep 24, 2006 #4
    bump. any feedback appreciated.
     
  6. Sep 25, 2006 #5

    Astronuc

    User Avatar
    Staff Emeritus
    Science Advisor

Share this great discussion with others via Reddit, Google+, Twitter, or Facebook