Vo=5m/s,a=-0.4m/s^2,S=30m
S=Vo*t+(1/2)at^2
30=5t(0.5)*(-0.4)t^2
t^2-25+150=0
(t-10)(t-15)=0
t1=10s
t2=15t
讨论:
速度减至0所需时间T=(0-Vo)/a=(0-5)/(-0.4)=12.5s
t2>T,不合题意,舍去
所求时间为t=10s