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ValeryOchkov24-Ruby IV
24-Ruby IV
August 27, 2012
Solved

One task - how can I use not rkfixed but odesolve?

  • August 27, 2012
  • 25 replies
  • 12533 views

A Task.

A steel core thrown vertically upward at a speed v0 and fell to the ground in 15 seconds. What is the coefficient of air resistance in the equation Ffriction = k S Ro v ^ 2? [The answer k=0.877 ]

I have a solution with the using the rkfixed function (Mathcad Prime with UNITS!- see the attach). In Mathcad 15 we can not use units in this task

1. Is the solution correct?

2. How can I use not rkfixed but odesolve function?

3. I'll take the other comments and suggestions gratefully!

t15.png

Best answer by ValeryOchkov

AlanStevens wrote:

Nearest I can manage.

Alan

Thanks for the idea.

I think it is a solution:

t15-d.png

25 replies

ValeryOchkov24-Ruby IVAuthor
24-Ruby IV
August 27, 2012

Problems with odesolve - see the attach.

AndyWesterman12-Amethyst
12-Amethyst
August 27, 2012

Ode solved?

Problem may be redefinition of 'm'

Regards

Andy

ValeryOchkov24-Ruby IVAuthor
24-Ruby IV
August 27, 2012

A Westerman wrote:

Ode solved?

Problem may be redefinition of 'm'

Regards

Andy

Thanks!

But:

t15blue.png

ValeryOchkov24-Ruby IVAuthor
24-Ruby IV
August 29, 2012

Eureka! I thought of Archimedes!

Eureka.png

ValeryOchkov24-Ruby IVAuthor
24-Ruby IV
August 29, 2012

So Mathcad calculates faster, but we do not understand how to get this equation:

Eureka-Simplify.png

AlanStevens19-Tanzanite
19-Tanzanite
August 29, 2012

Valery Ochkov wrote:

So Mathcad calculates faster, but we do not understand how to get this equation:

Eureka-Simplify.png

Haven't you got a y'(t) too many here Valery? i.e. shouldn't y'(t)^2.sign(y'(t)) be just y'(t).sign(y'(t))?

Alan

ValeryOchkov24-Ruby IVAuthor
24-Ruby IV
August 29, 2012

AlanStevens wrote:

Valery Ochkov wrote:

So Mathcad calculates faster, but we do not understand how to get this equation:

Eureka-Simplify.png

Haven't you got a y'(t) too many here Valery? i.e. shouldn't y'(t)^2.sign(y'(t)) be just y'(t).sign(y'(t))?

Alan

Sorry I do not understand your question!

y'^2.sign(y') is equal y'*|y'| - the vector of the friction force is opposite the vector of velosity!

But what is fester?

ValeryOchkov24-Ruby IVAuthor
24-Ruby IV
August 29, 2012

...and what about this:

- http://en.wikipedia.org/wiki/Inertial_frame_of_reference

and

- http://en.wikipedia.org/wiki/Non-inertial_reference_frame

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