一列火车从静止开始做匀加速直线运动,一个人站在第一节车厢前观

搜题请搜索小程序“爱下问搜题”

问题选择题

一列火车从静止开始做匀加速直线运动,一个人站在第一节车厢前观察,第一节车厢经过他历时2 s,全部列车经过他历时6 s,那么火车共有车厢( )

A．3节

B．7节

C．9节

D．10节

答案

答案：C

由初速度为零的匀加速直线运动位移公式s=at²可得,一节车厢的长度l₁=a×2²=2a,整列车厢的长度l=a×6²=18a,则火车共有车厢的节数n==9,故C正确.

选择题

— Mom, the door ____. My keys are locked in it again.

— You ____ it! I told you always to carry your keys with you. [ ]

A. can't open; have asked for

B. wouldn't be opened; asked for

C. won't open; asked for

D. can't be opened; are asking for

单项选择题

转炉的炉型是指（）。

A、炉壳形状

B、炉衬内型

C、炉子容积

D、停炉时的炉况