Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Falling from a Tree

  1. Jul 10, 2005 #1
    While exploring the canopy of the rainforest in equatorial South America, Anastasia falls from a branch 31.0 meters high. Exactly 1.4 seconds later Joe falls from the same branch. How high above the ground is Joe when Anastasia splats into the mud below? undefined
  2. jcsd
  3. Jul 10, 2005 #2
    this sounds almost to easy.

    y = y0 -1/2 * g* t ^2

    y = 31 - 1/2 * 9.8 * (1.4) ^ 2

    do the math
  4. Jul 10, 2005 #3
    I get 21.40m (21.396 m) but the computer I am doing it on cross checks my answer and says its wrong...
  5. Jul 10, 2005 #4


    User Avatar
    Science Advisor

    Yes, it was too easy. That is Anastasia's height when Joe starts to fall. To find Joe's height when Anastasia hits the ground:

    1) Solve 31- (1/2)(9.8)t2 to find time t when Anastasia hits the ground.

    2) Put that value of t into h= 31- (1/2)*(9.8)(t- 1.4)2 to find Joe's height h.
  6. Jul 10, 2005 #5
    i didnt want to do the whole problem for them, but yes halls is right
  7. Jul 15, 2005 #6


    User Avatar
    Homework Helper

    For what time Joe is in motion when Anastasia splats in mud??? is it 1.4 sec ??????
  8. Jul 16, 2005 #7


    User Avatar
    Science Advisor

    No, as I said before, solve (1/2)(9.8)t2- 31= 0 (her height will be 0) to find when Anastasia hits the ground.
  9. Jul 16, 2005 #8
    This is Anastasia's height. I'm trying to find Joe's...
  10. Jul 16, 2005 #9
    joe's height will be
    hjoe = 31 - (1/2)*(9.8)(TA - 1.4)^2
    where TA is when A hits the mud found by solving
    (1/2)(9.8)(TA)^2 = 31
  11. Jul 17, 2005 #10


    User Avatar

    StotleD: First I calculated how long it takes Anastasia to fall before hitting the ground. I came up with 2.52 seconds. If Joe falls 1.4 s after Anastasia does, and if she hits the ground after 2.52 s, then he has fallen for 1.12 s when she hits. You can calculate his distance fallen of distance above the ground or both. I got 6.15 m that Joe fell. 31.0 m - 6.15 m is the height above the ground: 24.85 m. Does that help and match your understanding and calculations?
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook