求助一个棒的震动问题

pyyzxxy

一端固定一端自由的棒，在初始时刻使棒具有位移y|<FONT size=1>t=0</FONT>=(y<FONT size=1>0</FONT>/l)x,求棒的横振动的位移表示<BR>这个初始条件应该怎么加呢？总是算不出来……

funi

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<TD class=text><IMG src="http://physics.bnu.edu.cn/include/elearn/physics/lxmn/up/2097449.gif" border=0> <BR><BR>令y1=θ，y2=dθ/dt则上式成为 <BR>dy1/dt=y2 <BR>dy2/dt=-3*k/（4*（M+3*m））y1 <BR></TD></TR></TABLE></TD></TR>
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<P>程序清单： </P>
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<P>functionthgzd <BR>theta0=pi/10;globallmMkg; <BR>m=1;M=2;k=80;g=9.8;l=2; <BR>[t,u1]=ode45(@thbfun,[0:0.05:15],[l0theta00]); <BR>[x1,y1]=pol2cart(u1(:,3),u1(:,1)); <BR>figure <BR>ymax=max(abs(y1)); <BR>axis([-13-2*ymax2*ymax]); <BR>axisoff <BR>holdon <BR>fori=1:length(t)-1 <BR>line([0.51.5],[2*ymax2*ymax],'color','r','linewidth',2);%%画弹簧上端连接的杆 <BR>line([0l*cos(u1(i,3))],[0,l*sin(u1(i,3))],'color','r','linewidth',2);%%画振动杆 <BR>line(x1(i),y1(i),'color','r','marker','.','markersize',70,'erasemode','xor');%%画小球 <BR>spring(l*cos(u1(i,3))/2,l*sin(u1(i,3))/2,1,2*ymax);%画弹簧 <BR>drawnow;pause(0.003); <BR>cla <BR>end <BR>%%画所规定时间的最后一刻的图形 <BR>line([0.51.5],[2*ymax2*ymax],'color','r','linewidth',2) <BR>line([0l*cos(u1(i+1,3))],[0,l*sin(u1(i+1,3))],'color','r','linewidth',2) <BR>line(x1(i+1),y1(i+1),'color','r','marker','.','markersize',70,'erasemode','xor') <BR>spring(l*cos(u1(i,3))/2,l*sin(u1(i,3))/2,1,2*ymax) <BR>drawnow <BR><BR><BR><BR>functionF=thbfun(t,u) <BR>globallmMkg; <BR>F=[0; <BR>0; <BR>u(4); <BR>-3*k*u(3)/(4*(M+3*m))]; <BR><BR><BR>functionspring(x0,y0,x1,y1) <BR>[a,r]=cart2pol(x1-x0,y1-y0); <BR>xx=0:r/200:r; <BR>yy=cos(30*pi*xx./r)/20; <BR>[a4,r4]=cart2pol(xx,yy); <BR>a4=a4+a; <BR>[xx,yy]=pol2cart(a4,r4); <BR>xx=xx+x0;yy=yy+y0; <BR>line(x0,y0,'color','r','marker','.','markersize',20,'erasemode','xor'); <BR>line(x1,y1,'color','r','marker','.','markersize',20,'erasemode','xor'); <BR>line(xx,yy,'color','b','linestyle','-','markersize',10,'linewidth',1,'erasemode','xor'); <BR></P></TD></TR></TABLE>