题干

质量为m的小球由轻绳a和b分别系于一轻质细杆的A点和B点,如图,绳a与水平方向成θ角,绳b在水平方向且长为l,当轻杆绕轴AB以角速度ω匀速转动时,小球在水平面内做匀速圆周运动,则下列说法正确的是(   )

A:b绳拉力不可能为零

B:a绳的拉力随角速度的增大而增大

C:当角速度ω> gltanθ ,b绳将出现拉力

D:若b绳突然被剪断,则a绳的拉力一定发生变化

上一题 下一题 0.0难度 选择题 更新时间:2015-03-11 03:19:58

答案(点此获取答案解析)

C

同类题4

阅读理解

    Growing up in Wyoming,everyday life was an adventure—I spent my time camping,and exploring mountains. When I was little,my mom became the state's first female U.S. Marshall.I'll never forget how the local newspaper praised her for her success in a field that's traditionally run by men.Under her influence,I made up my mind to achieve something great.Now,I've become famous for sailing,a sport often considered "a man's world".

    Sailing is considered a hard-to-break-into sport.And,generally,there are only two ways to get into it—either through a strict sailing education that leads to experience or by growing up on the water and racing in the Olympics. Most of my teammates became professional sailors in one of these two ways but I skipped both.

    In the summer of 2008,I went to St.Croix through a college internship(实习)program focusing on educating locals about HIV and AIDs.There,I discovered my love for sailing.Then,SCA,a global hygiene(卫生保健)company, made the decision to support an all-female team,and when they began accepting applications,I knew it was the chance of a lifetime.I made it my task to become a part of the team.Even when it seemed like there were no positions left,I never gave up.

    After a stressful,two-year application process,I finally got the call.I moved to Lanzarote in the Canary Islands and began training with the team immediately.The process was physically,mentally and emotionally exhausting,but I finally achieved my goal.I sailed in the "Everest of sailing" with only six years' experience.Later,there was an all-female team competing,and I was lucky enough to be a part of it.

    As women,we need to approach our dreams as if we deserve to achieve them as much as men,because we do. There are plenty of professions,including sailing,in which women are absent or have a minor presence—but that's not because they shouldn't be there.We need to push the boundaries and focus on obtaining our goals and passions,no matter how unobtainable and challenging they may seem.