HW4

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smefix
Beiträge: 83
Registriert: 23.10.2012, 18:54

HW4

Beitrag von smefix » 13.11.2016, 12:19

This is the question sheet and my solution. If anyone finds a mistake, feel free to tell me :D

This is the corrected version: I corrected Example 1, because I wrote the wrong vector for \vec{f_{m}}. Sry for that
I also corrected example 2, I hope that future examples will be more specific.
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Zuletzt geändert von smefix am 16.11.2016, 22:05, insgesamt 2-mal geändert.

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_Hofi_
Beiträge: 24
Registriert: 29.01.2015, 19:04

Re: HW4

Beitrag von _Hofi_ » 13.11.2016, 19:30

I dont know why your fm got multiplied by (-cos;sin;0)?
At the beginning you wrote f(vector)= (-fm;0;0) ;) and thats correct. On your local coordinate system fm(vector) should not change its angle!

tola99
Beiträge: 102
Registriert: 28.03.2012, 16:24

Re: HW4

Beitrag von tola99 » 14.11.2016, 23:52

could you explain me why you put in the second part of the second example T=0 in your first step? shouldnt it be only T_0=0?
thanks in advance!!

smefix
Beiträge: 83
Registriert: 23.10.2012, 18:54

Re: HW4

Beitrag von smefix » 15.11.2016, 11:00

_Hofi_ hat geschrieben:I dont know why your fm got multiplied by (-cos;sin;0)?
At the beginning you wrote f(vector)= (-fm;0;0) ;) and thats correct. On your local coordinate system fm(vector) should not change its angle!
thanks, it was late at night I guess :wink: I will correct my solution in a second

smefix
Beiträge: 83
Registriert: 23.10.2012, 18:54

Re: HW4

Beitrag von smefix » 15.11.2016, 13:11

tola99 hat geschrieben:could you explain me why you put in the second part of the second example T=0 in your first step? shouldnt it be only T_0=0?
thanks in advance!!
Next to the sketch of example 2 there is T \left( t \right) drawn. I was also confused at the very beginning. I don't know if this is how it was ment to be.
If you take T(t) as unknown, you would get the same result as in the first part, but every term that has T-T_{0} in it, you only would get T instead. And then you have to correct your constants as well. I was not sure about that, so I am going to ask the Prof. on Wednesday

tola99
Beiträge: 102
Registriert: 28.03.2012, 16:24

Re: HW4

Beitrag von tola99 » 15.11.2016, 14:36

smefix hat geschrieben:
tola99 hat geschrieben:could you explain me why you put in the second part of the second example T=0 in your first step? shouldnt it be only T_0=0?
thanks in advance!!
Next to the sketch of example 2 there is T \left( t \right) drawn. I was also confused at the very beginning. I don't know if this is how it was ment to be.
If you take T(t) as unknown, you would get the same result as in the first part, but every term that has T-T_{0} in it, you only would get T instead. And then you have to correct your constants as well. I was not sure about that, so I am going to ask the Prof. on Wednesday
Thanks a lot, had the same thoughts like you! I calculated it both ways, for me your solution looks better, but i'm confused because we did it in the tutorial that we said T_0 is zero after the stimulus, and it would be also more logical to me, if after the stimulus T_0 ends, there is still some kind of tension which is then decreases. but you're right about the sketch so i is really confusing.....

Grinsekatze
Beiträge: 35
Registriert: 09.05.2012, 18:59

Re: HW4

Beitrag von Grinsekatze » 15.11.2016, 19:12

T0 is just some "additional" tension provided by the tensile element, which counteracts the tension applied.
The graph provided in the homework tells us that someone "pulls" at the end of the muscle element and then lets go.
I guess the "boundary condition" of T(t=c) = 0 is irrelevant here, because we are looking at the displacement x instead of the tension T, and it makes sense to assume the initial tension affects the displacement of the spring, which will take a while to swing back into its initial position.

smefix
Beiträge: 83
Registriert: 23.10.2012, 18:54

Re: HW4

Beitrag von smefix » 16.11.2016, 18:07

Grinsekatze hat geschrieben:T0 is just some "additional" tension provided by the tensile element, which counteracts the tension applied.
The graph provided in the homework tells us that someone "pulls" at the end of the muscle element and then lets go.
I guess the "boundary condition" of T(t=c) = 0 is irrelevant here, because we are looking at the displacement x instead of the tension T, and it makes sense to assume the initial tension affects the displacement of the spring, which will take a while to swing back into its initial position.
Today I asked the prof. about this and he said, that as long it is not explicitly written that the muscle is pulled with a force T, it should be zero. So the sum of all three forces is 0.
However, if there was a force T we would need it's exact time dependency, or it is constant in order to solve the differential equation.
Since it is bit written here it should be constant and with the prof. Advice it is constant zero.
I will correct my solution this evening.

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