M={{0, 0, 1}, {0, 0, 1/(
  1/2 + l)}, {-(\[Omega]1^2/(
   2 (1/2 - (8 (-2 + \[Pi]))/((1 + 2 l) \[Pi]^3)))), -(
   2/((1/2 - (8 (-2 + \[Pi]))/((1 + 2 l) \[Pi]^3)) \[Pi])), 0}}

g(t)={0, p[t]/(
 1/2 + l), (-(
     16/((1 + 2 l) (1/2 - (
        8 (-2 + \[Pi]))/((1 + 2 l) \[Pi]^3)) \[Pi]^3)) +
    8/((1 + 2 l) (1/2 - (
       8 (-2 + \[Pi]))/((1 + 2 l) \[Pi]^3)) \[Pi]^2)) Derivative[1][
   p][t]}