#include <bits/stdc++.h>
double mymin(double a, double b) {
  if (a < 0)
    return b;
  else
    return a < b ? a : b;
}
int main() {
  double x1, y1, x2, y2;
  scanf("%lf %lf %lf %lf", &x1, &y1, &x2, &y2);
  double x, y;
  x = x2 - x1;
  y = y2 - y1;
  double v, t;
  scanf("%lf %lf", &v, &t);
  double vx, vy, wx, wy;
  scanf("%lf %lf %lf %lf", &vx, &vy, &wx, &wy);
  vx = -vx;
  vy = -vy;
  wx = -wx;
  wy = -wy;
  double r = -1;
  {
    double a = v * v - vx * vx - vy * vy;
    double b = -2 * (x * vx + y * vy);
    double c = -(x * x + y * y);
    if (b * b - 4 * a * c >= 0) {
      double s1 = (-b + sqrt(b * b - 4 * a * c)) / 2 / a;
      if (0 <= s1 && s1 <= t) r = mymin(r, s1);
      double s2 = (-b - sqrt(b * b - 4 * a * c)) / 2 / a;
      if (0 <= s2 && s2 <= t) r = mymin(r, s2);
    }
  }
  {
    double kx = x - wx * t + vx * t;
    double ky = y - wy * t + vy * t;
    double a = v * v - wx * wx - wy * wy;
    double b = -2 * (wx * kx + wy * ky);
    double c = -(kx * kx + ky * ky);
    if (b * b - 4 * a * c >= 0) {
      double s1 = (-b + sqrt(b * b - 4 * a * c)) / 2 / a;
      if (t <= s1) r = mymin(r, s1);
      double s2 = (-b - sqrt(b * b - 4 * a * c)) / 2 / a;
      if (t <= s2) r = mymin(r, s2);
    }
  }
  printf("%.20lf", r);
  return 0;
}
