Falling from a Tree

  • Thread starter StotleD
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  • #1
StotleD
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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
 

Answers and Replies

  • #2
mathmike
208
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this sounds almost to easy.

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

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

do the math
 
  • #3
StotleD
21
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I get 21.40m (21.396 m) but the computer I am doing it on cross checks my answer and says its wrong...
 
  • #4
HallsofIvy
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mathmike said:
this sounds almost to easy.

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

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

do the math

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.
 
  • #5
mathmike
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i didnt want to do the whole problem for them, but yes halls is right
 
  • #6
mukundpa
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For what time Joe is in motion when Anastasia splats in mud? is it 1.4 sec ?
 
  • #7
HallsofIvy
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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.
 
  • #8
StotleD
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This is Anastasia's height. I'm trying to find Joe's...
 
  • #9
geosonel
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StotleD said:
This is Anastasia's height. I'm trying to find Joe's...
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
 
  • #10
DAS
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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?
DAS
 

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