System of Differential Equations - How to solve?

[vlehner]

Hello,

Attached you can see a solve block with a system of Differential Equations.

Has somebody an idea what is wrong or is it a typical Prime-problem-if then it should be fixed in Prime 4.0?

I tried to solve completely without units but then i got the same error message again.

I am working with MathCad Prime 3.1

Thank you for your efforts.

regards

Volker

[-MFra- · Accepted solution]

Hi Volker,

what do you think about my solution shown in the following picture?

[vlehner]

Hi!

Wow, you got a solution.

you replaced x''(t) from the first Equation into the second Equation-and it works- can't belive it.

Why does MathCad don't accept my first solution?

Thank you!!!

[-MFra-]

Hi Volker,

Perhaps to define two times the second derivative of the same function, it creates difficulties.

since the argument I always liked (Lagrange equations) could you give me a sketch of the mechanical system (which seems like a pendulum, or something like that)?

In any case Thanks.

FM

[vlehner]

Hi FM,

The pendulum see attachement.

It is a roller-pendulum (=Rollpendel)

Have Fun!

regards Volker

ps.: And yes, Lagrangesche Formulas are great because many mechanical problems are easy to solve- I like it too

[-MFra-]

Hi Volker.

I thought that the problem was something strange or new, but

I see that it is an example that is on all texts of rational mechanics.

Anyway thank you very much.

FM

[vlehner]

Hi FM,

Next day i'll post a really strange mechanical problem where i have the same Problem.