题干

在做“研究匀变速直线运动”的实验中:

已知打点计时器所用交流电的频率为50Hz.如图所示为实验所打出的一段纸带,在顺次打出的点中,从O点开始每5个打点间隔取1个计数点,分别记为A、B、C、D.相邻计数点间的距离已在图中标出,则打点计时器打下计数点C时,小车的瞬时速度v=____m/s;小车的加速度a=____m/s2

上一题 下一题 0.0难度 选择题 更新时间:2016-02-22 05:02:35

答案(点此获取答案解析)

0.23,0.40

同类题2

阅读理解

    Nowadays, parents worry a lot because their children spend hours and hours in front of the TV screen. Because this doesn't happen to only one specific family, many experts warn us that there can be some serious effects of children watching violence on television.

    Children who become addicted(上瘾的) to TV sit down and turn on the TV as soon as they get home. Although they have lots of homework, they become absorbed in TV programs.

    Since they spend tons of time watching TV, they have less time to enjoy real life activities such as playing with friends, playing outdoor sports, or enjoying other kinds of entertainment.

    There are too many violent scenes on TV. Some experts say there are 25 acts of violence per hour on TV. In addition, there are many experiments by psychologists which show how TV violence influences children. Finally, people worry that children tend to imitate what they watch on TV and may start to behave more violently.

    What should be done? First of all, the government should regulate TV violence. It should also encourage people to invent and develop new technology which can block violent scenes from the programs children watch. For example, with a rating system(分级制度) and the V-chip, unfit scenes of violence and sex can be blocked out. Second, parents should monitor what their children watch. At the same time, they should make their children interested in real life activities. Then when the children start to spend more time playing with friends or reading books, parents can stop their monitoring.

    It is a fact that there is more violence on TV today than there was ten years ago. Moreover, violent incidents occur more frequently in real life. It's time to realize how harmful watching TV violence is, and it's time to keep our children from watching violence.

同类题3

任务型阅读

    Why do many people play sports? You might say “to get exercise'' and you'd be right. To have fun? That's true, too. But there's more.____According to the Women's Sports Foundation, girls who play sports get a lot more than just fit.

    Girls who play sports do better in school. ____But research shows that girls who play sports do better in school than those who don't. Exercise improves learning, memory, and concentration, which can give active girls an advantage in the classroom.

    Girls who play sports learn teamwork and goal-setting skills. Sports teaches valuable life skills. When you working with coaches, trainers, and teammates to win games and achieve goals, you're learning how to be successful. ____

    Sports are good for a girl's health. In addition to being fit and maintaining a healthy weight, girls who play sports are also less likely to smoke. And later in life, girls who exercise are less likely to get breast cancer.

    ____ Girls who play sports feel better about themselves. Why? It builds confidence when you know you can practice, improve, and achieve your goals. Sports are also a feel-good activity because they help girls get in shape, maintain a healthy weight, and make new friends.

    Exercise cuts the pressure. Playing sports can lessen stress and help you feel a little happier. How? ____ Friends are another mood-lifter. And being on a team creates tight bonds between friends. It's good to know your teammates will support you—both on and off the field!

A. Please take action to play games.

B. Playing sports boosts self-confidence.

C. Playing sports is good for your grades.

D. In fact, there are at least 5 more reasons.

E. Those skills will serve you well at work and in family life.

F. You might think that athletics will take up all your study time.

G. The brain chemicals released during exercise improve a person's mood.