What do I do next to solve for m?

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Amy Joyce Valencia 2021-10-22

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1569828-what-do-i-do-next-to-solve-for-m

评论： Star Strider 2021-10-23

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clear

syms f m g L I

E = 2*pi*f == sqrt((m*g*L)/I)

E =

%What is the mass when...

m = solve(E,m)

Warning: Solutions are only valid under certain conditions. To include parameters and conditions in the solution, specify the 'ReturnConditions' value as 'true'.

m =

subs(E, f ,0.1);

subs(E, I, 50);

subs(E, g, 9.8);

subs(E, L, 0.5);

Now I need to find a value for m but I'm not sure how to move forward with it

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Answer 1

Star Strider 2021-10-23

1
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https://ww2.mathworks.cn/matlabcentral/answers/1569828-what-do-i-do-next-to-solve-for-m#answer_814508

在 MATLAB Online 中打开

The conditions only apply if the values of the constants are not defined first.

Try this —

syms f m g L I

f = sym(0.1);

I = sym(50);

g= sym(9.81);

L = sym(0.5);

E = 2*pi*f == sqrt((m*g*L)/I);

m = solve(E,m)

m =

m_vpa = vpa(m, 42)

m_vpa =

4.02430352745743470696615331289547446903719

.

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Amy Joyce Valencia 2021-10-23

Do I have to use syms for every valuable? Or is there a way to shorten it?

Star Strider 2021-10-23

在 MATLAB Online 中打开

It’s not necessary to use the Symbolic Math Toolbox at all —

f = 0.1;
I = 50;
g = 9.81;
L = 0.5;
E = @(m) 2*pi*f - sqrt((m*g*L)/I)                           % Anonymous Function
E = function_handle with value:
    @(m)2*pi*f-sqrt((m*g*L)/I)
m = fzero(E, 10)
m = 4.0243