# Bungee jump -> differential equation -> simulink simulation

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1. Jan 11, 2016

### Wesker

Hello guys, I found this forum using google because I need help with simulating bungee jump model.
I've already done that with zero initial values and it looks good but I want it more realistic :
Let's say L is the lenght of rope so elasticity force starts acting when y=L so logically time should be
t(L) = sqrt(2*g*L)
I think that if t >=t(L) all forces should be acting togheter until there is not balance between them..
Canonical form is : y''(t) = g - B/m*y'(t) - k/m*y(t)
B - air resistance
m - jumper weight
k - elasticity ratio
I'm including screenshot of model I simulated so far...
What am I supposed to edit ?

#### Attached Files:

• ###### bungeejump.png
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2. Jan 11, 2016

### Wesker

+ I can't figure out why in some point velocity and acceleration goes below zero... If someone could explain me resp. guide me how to correct it I'd be really glad :)
Values I used :
B = 13.08
m = 80
k = 2.83

3. Jan 12, 2016

### Wesker

Ok I solved it with switch... and btw t(L) = sqrt(2*g*L) this is wrong as there is also air resistance..