#include <bits/stdc++.h>
using namespace std;
double x1, Y1, x2, y2, x, y, v, t, vx, vy, wx, wy, a, b, c, delta;
double solve() {
  x = x2 - x1;
  y = y2 - Y1;
  a = vx * vx + vy * vy - v * v;
  b = 2 * (x * vx + y * vy);
  c = x * x + y * y;
  delta = b * b - 4 * a * c;
  if (delta < 0.0) return -1.0;
  double ans1 = (-b + sqrt(delta)) / (2 * a);
  double ans2 = (-b - sqrt(delta)) / (2 * a);
  if (ans1 >= 0.0 && ans1 <= t) return ans1;
  if (ans2 >= 0.0 && ans2 <= t) return ans2;
  double xx1 = x + (vx - wx) * t;
  double yy1 = y + (vy - wy) * t;
  a = wx * wx + wy * wy - v * v;
  b = 2 * (xx1 * wx + yy1 * wy);
  c = xx1 * xx1 + yy1 * yy1;
  delta = b * b - 4 * a * c;
  if (delta < 0.0) return -1.0;
  ans1 = (-b + sqrt(delta)) / (2 * a);
  ans2 = (-b - sqrt(delta)) / (2 * a);
  if (ans1 >= t) return ans1;
  if (ans2 >= t) return ans2;
  return -1.0;
}
int main() {
  cin >> x1 >> Y1 >> x2 >> y2 >> v >> t >> vx >> vy >> wx >> wy;
  vx = -vx;
  vy = -vy;
  wx = -wx;
  wy = -wy;
  double ans = solve();
  printf("%.8lf\n", ans);
  return 0;
}
