o.k. i get it now. we are propagating a to limit the forces so the block/animal launched doesn't break/die. so that's why we pull out x from kx^2=ma then plug x into Uel=Ug. the objective again it to limit. then after we get the final equation, we can pick a k and an x-compression that will work.
The question is shown below the --- or this question and answerbook is from U Physics 12E #7.71. I uploaded a JPG that can be seen at http://i43.tinypic.com/35j9jja.jpg
I don't understand this problem. I see that to solve this Conservation of Energy and N2L are merged using x, and that h from...
o.k., i typed it here, but it's cryptic with (subscripts)
these four N2L equations:
-f = m(s) a(s)
F(ns) -F(Nb) -m(s)g = 0
f - F = m(b) a(b)
F(Nb) - m(b) g
are shown in the soln to resolve to
f = ( m(s) F ) / ( (m(s) + m(b) )
where do i begin ?
I already understand the problem, but am having trouble with the algebra for textbook Fund of Physics Solutions, Halliday, 8e, Ch6 Prob 34. Copied here
http://i56.tinypic.com/20uwhw4.jpg
I've been staring at this solution to N2L for hours and can't figure out how to go from the top 4 N2L...
O.K. I got it now, thanks for your help ;-)
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Yf= Yo + VoyT - .5gT^2
0 = 5280 - 12(427 - T) - 16T^2
= 5280 - 5124 + 12T - 16T^2
= -156 + 12T - 16T^2
the roots are -2.77, +3.51, and 3.51 is the RIGHT answer...
i manually figured out that for Sky#2 to fall 5280 ft, it takes T = 3.5 secs
5280 = 12(427 - T) + (16 * T^2)
next i tried with variable T
5280 = 12(427 - T) - 16T^2)
5280 = 5124 - 12T -16T^2
= -156 -12T -16T^2
the root is -.375, and it's wrong
but if i manually change it...
from 0-2 sec (.5 x 32 x 2^2)= 64 ft
5280 ft - 64 ft = 5216 ft
5216 ft / 12 ft/s = 435 sec
so sky1 takes 435 + 2 = 437 secs to hit ground
sky2 jumps 10 secs later 437 - 10 = 427 secs
5280 = 0 + ( 12 x (427 - T)) + (.5 x 32 T^2)
the last quadratic didn't work. hmm...
Homework Statement
Skydiver #1 from the University Skydiving Club steps out of a plane when it is 1 miles above the ground and 10 seconds later skydiver #2 steps out of a plane (at the same height).
They both want to land on the ground at the same time.
To make an estimate assume that...