grav.mws

>    deq1:=diff(x(t),t,t)=-M*g*x(t)/(x(t)^2+y(t)^2)^(3/2); deq2:=diff(y(t),t,t)=-M*g*y(t)/(x(t)^2+y(t)^2)^(3/2);

deq1 := diff(x(t),`$`(t,2)) = -M*g*x(t)/(x(t)^2+y(t)^2)^(3/2)

deq2 := diff(y(t),`$`(t,2)) = -M*g*y(t)/(x(t)^2+y(t)^2)^(3/2)

>    with(DEtools):

>    M:=6e24; g:=6.67e-11;

M := .6e25

g := .667e-10

>    dsolve([deq1,deq2],[y(t),x(t)]); 

Warning, computation interrupted

>    DEplot3d([deq1,deq2],[y(t),x(t)],t=0..7000,
[[y(0)=6.371e6,x(0)=0,D(y)(0)=0,D(x)(0)=-9000]],scene=[t,x(t),y(t)],stepsize=10,linecolor=t,orientation=[0,90]);

[Maple Plot]

>