plot the system of three equations

6 次查看（过去 30 天）
Kseniia Kudriavtceva
编辑： Stephan 2020-11-1
I have a Dynamics problem, which I solved and I have three eqations with three unknows.
I'm pretty sure in this part of a code:
% Given
syms theta
W_A=100;
m_A=W_A/32.2;
W_B=20;
m_B=W_B/32.2;
L=15;
theta_0=70;
% Solve the system of three equations
syms theta_1 V_A V_Bx
eq1 = W_A*L*(cos(theta)-cos(theta_0))-1/2*m_A*V_A^2-1/2*m_B*V_Bx^2+W_A*L;
eq2 = m_B*V_Bx+m_A*(V_Bx+L*theta_1*cos(theta));
eq3 = -V_A^2+(V_Bx+ L*theta_1*cos(theta))^2+(L*theta_1*sin(theta))^2;
But I need to have plots for V_A and V_Bx for theta [-70,70]. But what I do doesn't work as I need it to.
eqs = [eq1, eq2, eq3];
[theta_1,V_A,V_Bx]=vpasolve(eqs,[theta_1,V_A,V_Bx]);
% Plot the velocity of the trolley and the speed of the rider as a function of the angle θ of the first half of a full swing
fplot(V_Bx, [-70,70], 'Linewidth',2)
hold on
fplot(V_A, [-70,70], '-.*c')
hold off
Maybe You know what am I doing wrong?

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回答（1 个）

Stephan
Stephan 2020-11-1
编辑：Stephan 2020-11-1
% Given
syms theta
W_A=100;
m_A=W_A/32.2;
W_B=20;
m_B=W_B/32.2;
L=15;
theta_0=deg2rad(70);
% Solve the system of three equations
syms theta_1 V_A V_Bx
eq1 = W_A*L*(cos(theta)-cos(theta_0))-1/2*m_A*V_A^2-1/2*m_B*V_Bx^2+W_A*L;
eq2 = m_B*V_Bx+m_A*(V_Bx+L*theta_1*cos(theta));
eq3 = -V_A^2+(V_Bx+ L*theta_1*cos(theta))^2+(L*theta_1*sin(theta))^2;
eqs = [eq1, eq2, eq3];
[theta_1,V_A,V_Bx]=solve(eqs,[theta_1,V_A,V_Bx])
% Plot the velocity of the trolley and the speed of the rider as a function of the angle θ of the first half of a full swing
fplot(V_Bx, [-theta_0,theta_0], 'Linewidth',2)
hold on
fplot(V_A, [-theta_0,theta_0], '-.*c')
hold off

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