题干

空气对运动物体的阻力与物体运动快慢有关,物体运动越快,所受空气阻力越大.在高空竖直上抛的小球,球出手后上升到最高点又落回原地过程中,以下对其运动过程描述正确的是(  )

A:小球机械能保持不变

B:小球的惯性先减小后增大,最后不变

C:小球所受的合力不变

D:小球的速度先减小后增加,最后不变

上一题 下一题 0.0难度 选择题 更新时间:2018-01-10 09:35:31

答案(点此获取答案解析)

D

同类题5

阅读理解

    Sometimes the toughest thing about feelings is sharing them with others. Sharing your feelings helps you whether your feelings are wonderful or terrible. Sharing also helps you to get closer to people you care about and who care about you. But how?

    You can't tell your friends what's inside your backpack if you don't know what's in there yourself. Feelings are the same way. Before you can share them with anyone, you have to figure out what feelings you have.

    Making a list of your feelings can help. You can do this in your mind or by writing it out or even by drawing pictures. Is something bothering you? Does it make you frustrated or terrified? Do you feel this emotion only once in a while or much of the time?

    The way a person feels inside is important. If you keep feelings locked inside, it can even make you feel sick! But if you talk with someone who cares for you, you will almost always start to feel better. It doesn't mean your problems and worries magically disappear, but at least someone else knows what's bothering you and can help you find solutions.

    Your mom and dad want t0 know if you have problems and what's happening in your life. But what if a kid doesn't want to talk with parents? Then find another trusted adult, like a relative or a teacher at school. Maybe this person can help you talk with your parents about your problem or concern.

    Once you know who you can talk with, you'll want to pick a time and place to talk. You can talk publicly in your family. But some kids are more private than others and they will feel shy about sharing their feelings. Then find a quiet place or write it down on a piece of paper. A kid doesn't have to share every feeling he or she has.