1. Limited time only! Sign up for a free 30min personal 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!

Finding a net force

  1. Dec 5, 2009 #1
    1. The problem statement, all variables and given/known data

    the questions says,
    "Person A who's mass is 40kg, is being pulled across the ground by a horse at a speed of 4 m/s [E]. All of a sudden the horse accelerates for a period of 5 seconds. During this time person A experiences a displacement of 40 m [E]. What net force was experienced by person A?"

    2. Relevant equations



    3. The attempt at a solution

    I have no idea how to even begin this question. I'm not sure what equations i even need to use.
     
  2. jcsd
  3. Dec 5, 2009 #2

    rl.bhat

    User Avatar
    Homework Helper

    Hi dois, welcome to PF.
    In the problem the initial velocity, duration pof acceleration and the displacement is given. Can find find a kinematic equation from the text book which relates these quantities with acceleration?
     
  4. Dec 5, 2009 #3

    AEM

    User Avatar

     
  5. Dec 5, 2009 #4
    ok so first I would need to find the acceleration so I can sub that answer into F= m*a
    so i would use
    acceleration= v/t
    ?
     
  6. Dec 5, 2009 #5
    The problem gives you the initial speed (Vi), time (t), and displacement (d). If you take a look at the kinematic equations, you'll find that you can solve one of them for acceleration. The kinematic equation you're looking for is this one.

    d = (vi)(t) + (1/2)(a)(t)^2

    Go from there.
     
  7. Dec 6, 2009 #6
    Ok so if we sub all of our know variables into the equation
    d = (vi)(t) + (1/2)(a)(t)^2
    then we would get:
    40= 4x5 +1/2 (?) x5^2
    40=20 +25/2 x
    20=25/2 x
    20=12 1/2 x
    x= 1.6

    but as soon as i figure out the acceleration where do I go from there to find out the net force?
     
    Last edited: Dec 6, 2009
  8. Dec 6, 2009 #7

    AEM

    User Avatar

    Okay, your algebra looks good, so a = 1.6 m/sec squared.

    Remember I said this was a two step question. Go back and read my first post. That indicates what you do next.
     
  9. Dec 6, 2009 #8
    So then we would sub a into F=ma
    so (40kg) (1.6 m/s)
    and then our answer would be Fnet= 64 kg m/s [E]
     
  10. Dec 6, 2009 #9

    AEM

    User Avatar

    That should do it, except that the units you give are wrong. The seconds should be squared. That combination of units has its own name: Newtons.
     
  11. Dec 6, 2009 #10
    alright, thank you!!
     
  12. Dec 6, 2009 #11

    AEM

    User Avatar

    You are quite welcome.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Finding a net force
Loading...