#Need help solving this second order differential equation

118 messages · Page 1 of 1 (latest)

verbal shard
#

It is about projectile motion with drag force
g is acceleration of free fall

If possible I want my solution in a form that link y to x and theta where

Left side only have y and right side only have x and theta and maybe times or add some constant(s)

formal pathBOT
verbal shard
#

@viral zephyr

viral zephyr
#

is this a differential equation in terms of y with respect to x?

#

or even a differential equation system

round schooner
#

Ru in uni ?

viral zephyr
#

because i never learnt how to solve systems 💀 yet

viral zephyr
round schooner
#

Which?

viral zephyr
#

uhmmmmmm wdym which

round schooner
#

Name ?

viral zephyr
round schooner
#

Nvm I sleep 3 am already got school in 2.5 hrs

viral zephyr
verbal shard
# viral zephyr ok i imagined something different uhmmm

Basically, you are suppose to change ax to d2x/dt^2
And change ay to d2y/dt^2 and that is how you form the equations. Then somehow get x in term of t and y in term of t. And maybe substitute t in x to y or the other way round to get y in term of x and theta.

viral zephyr
#

s'' = a

verbal shard
#

Yes.

viral zephyr
#

$a(t) = -kv(t) \Rightarrow \frac{d^2x}{dt^2}= -k \cdot ucos\theta \
a(t) =-g-k(t) \Rightarrow \frac{d^2y}{dt^2}= -g - usin\theta$

#

what is k_y ?

#

or it supposed to be v_y?

verbal shard
#

How did you do that?

viral zephyr
#

what

#

i deleted it as i wasnt sure what k_y is

verbal shard
#

K is like a constant.

viral zephyr
#

k_y ?

verbal shard
viral zephyr
#

but i was unsure

verbal shard
#

Wow. Maybe this is correct?

verbal shard
viral zephyr
#

ehm i dont think so

cobalt inletBOT
#

adonhs

verbal shard
#

Oh I see. I put wrong.

#

Sorry. I did not see properly.

#

For Ky I meant K.

#

So basically just K.

#

Both k in both equations have the same value.

viral zephyr
#

$a_x(t) = -kv_x(t) \Rightarrow \frac{d^2x}{dt^2}= -k \cdot ucos\theta \
\a_y(t) =-g-k\Rightarrow \frac{d^2y}{dt^2}= -g - k$

cobalt inletBOT
#

adonhs

verbal shard
viral zephyr
verbal shard
viral zephyr
#

$x''(t) = -k \cdot cos\theta$ and $y''(t) = -g-k$

cobalt inletBOT
#

adonhs

viral zephyr
#

i think we could differentiate

#

$v_x = ucos\theta \Rightarrow \frac{dx}{d\theta} = -usin\theta$?

cobalt inletBOT
#

adonhs

viral zephyr
#

if v_x is a function of theta

verbal shard
#

But I thought you need in function of t so that can substitute t later?

#

Because want y on the left side and x and theta on the right side.

viral zephyr
#

so we are working with vectors and matrices

#

and x and y are components

verbal shard
#

I never learnt those. Maybe just tiny bits of vector.

viral zephyr
#

or you do

verbal shard
#

For vector I onky know like the level of the person yesterday. I do not know about equations or planes.

#

Is that person called unknown?

viral zephyr
#

are you a high schooler?

verbal shard
#

I saw in a worksheet and that is exactly the level I am at.

verbal shard
viral zephyr
#

i thought u were some engineer ok lol

verbal shard
#

As you can see I am pre university.

viral zephyr
#

some people who study have pre uni and some who are high schooler have undergraduate role so cant tell

#

besides that i thought because it involves some physics lol

#

I would start off with this

cobalt inletBOT
#

adonhs

viral zephyr
#

because v_x is basically the first derivative of x(t)

verbal shard
#

I am trying to understand it.

viral zephyr
#

I would write it even simpler

verbal shard
#

From what I know to get x and y I have to integrate twice? But that does not seem correct?

#

Okay. This is rewriting equation?

viral zephyr
#

yes to my understanding

#

it should make sense that v_x = dx/dt = x' first derivative

#

a_x = d²x/dt² = x''

#

I would try to do this with this video

#

so basically we have

#

actually

cobalt inletBOT
#

adonhs

viral zephyr
#

In physics instead of ' we use dots if it's with respect to time

#

Maybe integrating both sides helps

cobalt inletBOT
#

adonhs

#

adonhs

#

adonhs

viral zephyr
#

Now this is the approach

cobalt inletBOT
#

adonhs

viral zephyr
#

So we can rewrite the equation as

verbal shard
#

I am completely lost.

cobalt inletBOT
#

adonhs

viral zephyr
#

It's just that I am familiar with linear algebra so I thought give it a try

#

So now we would for the Eigenvalues as this equation above reminds us of the Eigenvalues of a matrix

#

,w eigenvalues {{[//number:-0.5k//],[//number:C//]},{[//number:D//],[//number:-(g+k)//]}}

viral zephyr
#

I am gonna use the lambda notation for the eigenvalues

#

The Eigenvectors look so complicated haha

cobalt inletBOT
#

adonhs

viral zephyr
#

So basically the solutions should be

cobalt inletBOT
#

adonhs

viral zephyr
#

Hmm I honestly, I can't tell, since we have too many constant variables, we already had g and k, but due to the integration of both equations we also got C and D and the vectors c1 and c2 are also "vector of constants" and a and b are constants of the linear combination (linear algebra)

#

You'd need some basic foundation in Linear Algebra and Calculus/Analysis, at least to know what Eigenvalues and Eigenvectors are but anyway

#

This is all I could do LOL

#

Here is the link again:
https://www.youtube.com/watch?v=E0YUvCqhr-c

You could check some videos out of him or so

How to find eigenvalues: https://youtu.be/hpE9Iom55N0

When we start looking at how multiple quantities change, we get systems of differential equations. What do we use for systems of equations? Linear algebra, of course!

Full dissecting differential equations playlist: https://www.youtube.com/playlist?list=PLug5ZIRrShJF-vOxStdHg1jyntiTKrAYO

N...

▶ Play video
viral zephyr
#

x² instead of x...

#

well it was all for nothing i guesscatKing

#

Maybe you can check out the other channels people who are more experienced than me

#

#calculus
#real-complex-analysis
#advanced-analysis

#

you can try it in those channels, i believe they are connected to this topic

#

#diff-geo-diff-top should also work too

verbal shard
verbal shard
verbal shard