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!

Free-Fall Problem

  1. Sep 9, 2012 #1
    A rock dropped from a cliff falls one-third of its total distance to the ground in the last second of its fall. How high is the cliff?

    I'm not asking for answer, I know the Physics Forum rules, but I am totally unsure where to start. I guess I have to use the equation d = Vot + at²/2 ?

    Could you please give me a hand and help me figure it out, please. Hints is all I need. Thanks.
  2. jcsd
  3. Sep 9, 2012 #2
    lemme try

    you are given initial velocity =0
    acceleration is 10/9.8m/s2
    let total height be h
    and time taken to cover full length be t+1 sec

    now find distance travelled is t seconds and then find it for t+1 sec

    then u get 2 equations involving time and height

    solve for answers...
  4. Sep 9, 2012 #3
    Why t+1, though?
  5. Sep 9, 2012 #4
    now distance traveled in last sec is known

    so u can take total time as t and 1 sec before time time as t-1


    u can take total time as t+1 and 1 sec before time as t
  6. Sep 10, 2012 #5
    Or just solve for V_0 with d = 1/3 h and t = 1 s. Then go back and solve for the time it takes to attain that velocity in free fall.
  7. Sep 10, 2012 #6


    User Avatar
    Homework Helper

    h = 1/2*g*t^2 --------(1)
    h - h/3 = 1/2*g*(t - 1)^2 -------(2)
    Divide 1 by 2 and solve for t. Hence find h.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Similar Discussions: Free-Fall Problem
  1. Free-fall problem (Replies: 2)

  2. Free fall problem (Replies: 19)