const m = 0.0007, mu = 1.2e-6, C = 0.020, U0 = 250.0, R = 0.01;
/*       {t:t  , w:[  x, p_x, Q     , p_Q]}*/
let bc = {t:0.0, w:[0.2, 0.0, C * U0, 0.0]}
let ls = [
  (z) => {
    const  p_x = z.w[1];
    return p_x / m;
  },
  (z) => {
    const x   = z.w[0];
    const p_Q = z.w[3];
    const d   = p_Q / x;
    return 0.5 * d * d / mu;
  },
  (z) => {
    const x   = z.w[0];
    const p_Q = z.w[3];
    return p_Q / (mu * x);
  },
  (z) => {
    const x   = z.w[0];
    const Q   = z.w[2];
    const p_Q = z.w[3];
    const Rp  = - (R * p_Q) / (mu * x);    
    return Rp - Q/C;
  },
];
let r = solve (5.0e-7, 2000, bc, ls); /* řešení */

plot (r, {x:['t'],    y:['w', 1]}, '#00ff00');
plot (r, {x:['t'],    y:['w', 3]}, '#ff0000');
delete r.data; /* ukliď po sobě */