火车初速度为10m/s,关闭油门后前进150m,速度减为5m/s,再经过30s,火车前进的距离为(  ) A.50m B.37.5m C.150m D.43.5m

问题描述:

火车初速度为10m/s,关闭油门后前进150m,速度减为5m/s,再经过30s,火车前进的距离为(  )
A. 50m
B. 37.5m
C. 150m
D. 43.5m

由速度位移公式v2v02=2ax得,a=

v2v02
2x
25−100
2×150
m/s2=−0.25m/s2
列车停止还需的时间t0
0−v
a
−5
−0.25
s=20s

则30s内前进的距离等于20s内前进的距离.
x=vt0+
1
2
at02=5×20−
1
2
×0.25×400m=50m
.故A正确,B、C、D错误.
故选A.