问题 选择题

在平直公路上,汽车以20m/s的速度运动,从某时刻开始刹车,在阻力作用下,汽车以4m/s2的加速度做匀减速直线运动,则刹车后10s内汽车的位移大小为(  )

A.0

B.50m

C.150m

D.400m

答案

设汽车从刹车到停止运动的时间为t0.则由v=v0+at0=0得:

t0=

-v0
a
=
-20
-4
s=5s

刹车后5s汽车即停止运动,则刹车后10s内汽车的位移等于后5s内的位移,大小为:

x=

v0t0
2
=
20
2
×5
m=50m

故选B

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