✔ 最佳答案
設AB平行距離為x m則s^2 = 30^2 + x^22s(ds/dt) = 2x(dx/dt)ds/dt = (x/s)(dx/dt)AB速度差 = 18 – 15 = 3 m/s當s = 50 時, 50^2 = 30^2 + x^2 => x = 40 m因此 ds/dt = (40/50)(3) = 2.4 m/s 設A距離T x m, B y ms^2 = x^2 + y^2 2s(ds/dt) = 2x(dx/dt) + 2y(dy/dt)ds/dt = (x/s)(dx/dt) + (y/s)(dy/dt)當x = 120, y = 90 s^2 = 90^2 + 120^2 = 22500 => s = 150因x及y隨時間縮短, dx/dt 及dy/dt皆為負ds/dt = (120/150)(-20) + (90/150)(-15) = -25 m/s