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!

HELP free fall

  1. Sep 28, 2008 #1
    an object is thrown upwards, at the top of the path it has
    a) zero acceleration
    b) maximum momentum
    c) maximum kE
    d) is at equillibrium
    e)none of the above


    i know accelarion is 9.8m/s^2
    i also know is not KE since at the top is potential
    im confused of the other two
     
  2. jcsd
  3. Sep 28, 2008 #2

    LowlyPion

    User Avatar
    Homework Helper

    b) what is formula for momentum?
    d) what is equilibrium?
     
  4. Sep 28, 2008 #3
    those are the ones that i dont know i think momentum is = mv
     
  5. Sep 28, 2008 #4
    Ok, so if you know that P = mv, and the object is at the max height of its trajectory, then what would be it's velocity and momentum?
     
  6. Sep 28, 2008 #5
    v is zero
     
  7. Sep 28, 2008 #6
    ok vo is zero but the final velocity =v + gt but im confused
     
  8. Sep 28, 2008 #7

    gabbagabbahey

    User Avatar
    Homework Helper
    Gold Member

    yes, v=0 at the top, so what is the momentum at the top?
     
  9. Sep 28, 2008 #8
    0 but what about equllibrium
     
  10. Sep 28, 2008 #9

    gabbagabbahey

    User Avatar
    Homework Helper
    Gold Member

    look up the definition of mechanical equilibrium
     
  11. Sep 28, 2008 #10
    i dont get the definition is says something about rest but so does the free fall at top have equllibrium but then we only have one force gravity since air is neglected
     
  12. Sep 28, 2008 #11

    LowlyPion

    User Avatar
    Homework Helper

    OK. Is it at rest at the top?
     
  13. Sep 28, 2008 #12

    gabbagabbahey

    User Avatar
    Homework Helper
    Gold Member

    http://en.wikipedia.org/wiki/Mechanical_equilibrium

    "A rigid body is in mechanical equilibrium when the sum of all forces on all particles of the system is zero, and also the sum of all torques on all particles of the system is zero."

    What forces are at play here? Is the net force on the particle zero at the top of its path?
     
  14. Sep 28, 2008 #13
    there is only gravity
     
  15. Sep 28, 2008 #14
    i dont get equllibrium sorry :(
     
  16. Sep 28, 2008 #15
    Ok, try and think fundamentally. At the very top, the instantaneous velocity is zero. If the velocity is zero then the net acceleration must also be zero at that very instant. So if F = ma, then the net force must be zero too. If you are still confused, I frankly do not know how else to explain it.
     
  17. Sep 28, 2008 #16
    so at the top there is equllibrium even though there is only one force the sum will be concidered zero
     
  18. Sep 28, 2008 #17
    "If the velocity is zero then the net acceleration must also be zero at that very instant. So if F = ma,"
    but how does velocity applied in the equation f=ma
     
  19. Sep 28, 2008 #18
    but i thought that the acceleration was gravity and gravity was throughout the whole path
     
  20. Sep 28, 2008 #19

    gabbagabbahey

    User Avatar
    Homework Helper
    Gold Member

    That's incorrect, the velocity will be zero, but it will still be accelerating downwards; the net force will still just be the force due to gravity, which is nonzero.
     
  21. Sep 28, 2008 #20

    gabbagabbahey

    User Avatar
    Homework Helper
    Gold Member

    This thought is correct; see above^^^.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: HELP free fall
  1. Free fall help! (Replies: 4)

  2. Help With Free Fall (Replies: 8)

  3. Free Fall help (Replies: 1)

Loading...