> | deq:=diff(v(t),t)=g+a/m(t)-diff(m(t),t)/m(t)*v(t); |
> | m(t):=4*(R0+c*t)^3*Pi/3*rho; |
> | a:=-alpha*abs(v(t))*v(t); |
> | g:=10; R0:=0.001; c:=R0/10; rho:=1000; alpha:=1e-6; deq; |
> | with(DEtools): |
> | DEplot(deq,v(t),t=0..4,v=-2..14,[[v(0)=-2],[v(0)=2],[v(0)=6],[v(0)=10],[v(0)=14]],stepsize=0.1,colour=black,linecolor=[blue,yellow,black,red,green]); |
> |