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 question

  1. Nov 29, 2009 #1
    I am wondering if I did this right.

    1. The problem statement, all variables and given/known data

    An object falls a distance h from rest. If it travels 0.57h meters in the last 1.00 s,
    I need to know the time and the height of its fall.



    2. Relevant equations



    3. The attempt at a solution

    Here what I have:

    Since it traveled .57H meters in the last second, I used y=vt+.5gt^2, and got .57H=4.9 since the time elapsed is 1 second and it came from rest, so the inital velocity is zero. Then I solved for H, getting around 8.59 m. Then with this I set up 8.59=4.9t^2, and solved for T, getting around 1.325 seconds. Was these the right methods?
     
  2. jcsd
  3. Nov 29, 2009 #2

    HallsofIvy

    User Avatar
    Staff Emeritus
    Science Advisor

    Since, as you say, the initial velocity is 0, the distance traveled in t seconds is y= .5gt^2. But he "time elapsed" is NOT 1 second. You are told that the object travels 0.57h m in the last second but you don't know how many seconds it had fallen before that. You are assuming the object fell .57h m in the first second.

    Suppose it fell for a total of T seconds. Then it fell .57h meters between T-1 and T. In the first T-1 seconds it fell .5g(T-1)^2 and in all T seconds it fell .5gT^2 meters. During that last second, it fell .5gT^2- .5g(T-1)^2= .57h meters. And, of course, you have .5gT^2= h, the total distance fallen.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Free-Fall question
  1. Free variable (Replies: 5)

Loading...