For 10:24 , 當時行車速率大約60km/h的算式是(可能正確): Let the braking force of the car be 10,000N(assumption) and the mass of the car be 1500kg(assumption). By s=ut+(1/2)at^2, a=(v-u)/t, F=ma. 10000=1500a a=-6.6667m/s^2(take it be negative as it is deceleration) Put v=0m/s, s=20m, a=-6.6667m/s^2 6.6667=(0-u)/t t=u/6.6667s 20=u(u/6.6667)+(1/2)(-6.6667)(u/6.6667)^2 u=16.330m/s Changing unit, u=58.787km/h~60km/h Therefore, 當時行車速率大約60km/h.