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!

What is the average velocity of the object as it falls to the ground?

  1. Nov 21, 2009 #1
    1. The problem statement, all variables and given/known data
    An object is dropped from a height of 25m above the ground. What is the average velocity of the object as it falls to the ground?


    2. Relevant equations
    d=vit+1/2at^2


    3. The attempt at a solution
    d=-25
    a=-9.8
    vi=0

    -25=-4.9t^2
    t=2.3s
    vavg=displacement/time
    -25/2.3=-10.8m/s
    the answer in book says a=-11.1m/s i don't understand, please help?
     
  2. jcsd
  3. Nov 21, 2009 #2

    kuruman

    User Avatar
    Homework Helper
    Gold Member

    Use the 2.3 s time of flight to find the velocity just before the object hits the ground. Half of that (because the starting velocity is zero) is the average velocity.
     
  4. Nov 21, 2009 #3
    I still don't understand, how does that get plugged into the formula? What formula do I use?
    Thank you
     
  5. Nov 21, 2009 #4

    kuruman

    User Avatar
    Homework Helper
    Gold Member

    Use the kinematic equation that gives you the velocity of an object at any time t.
     
  6. Nov 21, 2009 #5
    v=d/t right?
     
  7. Nov 21, 2009 #6

    kuruman

    User Avatar
    Homework Helper
    Gold Member

    Nope. That equation is valid only when the acceleration is zero. Here the acceleration is g down. What equation do you know that relates the initial and final velocity to acceleration and time?
     
  8. Nov 21, 2009 #7
    a=vf-vi/t right?
     
  9. Nov 21, 2009 #8

    kuruman

    User Avatar
    Homework Helper
    Gold Member

    That's the one. You know everything except vf.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: What is the average velocity of the object as it falls to the ground?
Loading...