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!

Force and Momentum HELP

  1. Nov 7, 2007 #1
    Force and Momentum... HELP!!!

    1. A graph is given (Force/body weight vs time). The peak on the graph gives a maximum force of 2.2x the body weight, Suppose a 70kg runner with a stride of speed 4.5 m/s. The impact speed of a 70kg runners foot is measured with 1.5 m/s. The effective mass of the foot and lower leg is 4.2 kg. The shoe and heel compress the ground a distance of 1.cm upon impact. Estimate the peak impact force exerted by the food on the ground.



    2.Favg= delta P/impact time, impact time= [2(impact distance)/(impact velocity)]



    3. I plugged in 0.012m for the impact distance, 2.5 m/s for the impact velocity and got an impact time of 0.016 seconds, which im pretty sure is right. For the change in momentum i wasnt too sure on what to use (the mass of the person or the foot). I assumed the foot slammed into the ground and bounced back up so I did (4.2 kg)(1.5)(2). I got 12.6. I divided 12.6 by 0.016 since delta P/impact time is average force and got 787.5 N.

    I dont think I did this right since it should be (2.2)(70)(9.8) which is around 1000 N. Is my work wrong? Thanks!!!!
     
  2. jcsd
  3. Nov 8, 2007 #2
    i was thinking.... they wouldnt give the mass and velocity of the person for no reason right?
     
  4. Nov 9, 2007 #3
    can anyone helllp please?
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Force and Momentum HELP
  1. Force and Momentum (Replies: 1)

  2. Momentum and force (Replies: 5)

  3. Momentum to Force (Replies: 5)

Loading...