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“m dv/dt=-mg-kv v(0)=0” (Wherek=k_1)
This can be re arranged to dv/dt=-g-Dv/m, if we make –g the subject dv/dt+kv/m=-g
If we let only dv/dt and v be left in the equation and swap out all the other terms we can use an integrating factor. dv/dt+vL(t)=N(t) Where L(t)=k/m and N(t)=-g
This means v=1/u ∫▒〖N(t)u dt〗
Where u=e^∫▒L(t)dx =e^(k/m) dt =e^(k/m t)
This in turn means v=e^(-k/m t) ∫▒〖(-g)e^(k/m t) dt〗 or e^(k/m t) v=∫▒〖(-g)e^(k/m t) dt〗 e^(k/m t) v=(-gm)/k e^(k/m t)+C
To work out C we can use the initial condition v(0)=0 so t(0)=0 e^(k/m(0)) 0=(-gm)/k e^(k/m(0))+C
This means C=gm/k
Returning to the Full equation again e^(k/m t) v=(-gm)/k e^(k/m t)+gm/k v(t)=(-gm)/k+gm/k e^(--k/m t) v(t)=gm/k(e^(- k/m t)-1) For 0≤t
(as we are measuring velocity downwards to be negative when t becomes a great number the e^(-k/m t) gets smaller making the number negative.)
The position can be found by integrating the velocity, with the same conditions x(0)=0
P(t)=∫▒v(t) dt Or P(t)=∫▒〖(-gm)/k+gm/k e^(-k/m t) 〗 dt
P(t)=(-gm)/k t-(gm^2)/k^2 e^(-k/m t)+C
Again if we let P(0)=0 we are able to find C
P(0)=(-gm)/k (0)-(gm^2)/k^2 e^(-k/m(0))+C
P(0)=-(gm^2)/k^2 +C we can say P(0)=P_0
This means C=P_0+(gm^2)/k^2
Finally our equation for position becomes
P(t)=(-gm)/k t-(gm^2)/k^2 e^(-k/m t)+P_0+(gm^2)/k^2

“P(t)=P_0-gm/k t-(gm^2)/k^2 〖(e〗^(-k/m t)-1) 0≤t
Modelling the Deployed chute
As we had before we had the condition v(0)=0 we can now change that to v〖(t〗_0)=v_0 (as t0 is the time the parachute is deployed by the parachutist) v〖(t〗_0)=v_0=-mg/k-gAe^(-k/m t_0 )
Making A the subject A=-e^(-k/m t_0 ) (m/k+v_0/g)
If we Put A back into the or...

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...October 2013
“Acceleration of Gravity and Newton’s Second Law of Motion“, The Engineering ToolBox, < http://www.engineeringtoolbox.com/accelaration-gravity-d_340.html >, 3 October 2013
Blevins, Robert D. 2003. Applied Fluid Dynamics Handbook. Krieger Publishing Co.J. Drucker, Minimal time of descent, The College Mathematics Journal 26, 232±235 (1995).
C. H. Edwards, Jr. and D. E. Penney, Differential Equations and Boundary Value Problems:Computing and Modelling, Prentice Hall, 1996.
Terminal Velocity”, Designed and maintained by webscaping.co.uk ©, 2013, , 28 October 2013
“The Parachute Problem”, Noam Goldberg, Craig Kaplan and Tucker Riley, 2011, < faculty.oxy.edu/ron/math/341/10/projects/Goldberg-kaplan-Riley.ppt >, 3 October 2013

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