题干

 为了将放置在水平地面上重为100N的物体提升一定高度,设置了图1所示的滑轮组装置.当用图乙所示随时间变化的竖直向下的拉力F拉绳时,物体的速度v和物体上升的高度h随时间变化的关系分别如图丙和丁所示.(不计绳重和绳与轮之间的摩擦)下列计算结果正确的是(  )

A:0s~1s内,地面对物体的支持力是10N

B:1s~2s内,拉力F做的功是187.5J

C:2s~3s内,拉力F的功率是100W

D:2s~3s内,滑轮组的机械效率是62.5%

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B

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    If something that you’re doing doesn’t challenge you, then it doesn’t change you. We all need some normal stress in our lives, after all____ So challenge the following limits:

    Figure out what you’re scared of and do it continuously.

If you're a salesman,and you're scared of talking to people personally or over the phone, now, instead of being scared and thinking you’ll fail, spend at least five minutes a day to pick up the phone and make a call.____ But don’t stop on the first try! Eventually, you can look at fear in the eyes and say, “Go on, I'm not scared!”

    ____

    Make sure this hobby is not linked to your career; you have to relax and relieve your stress while performing this. Some examples might be cooking, sewing, painting and so on. Apart from helping you challenge yourself, taking a class for your hobby may also give you extra income.

    Set aside at least nine minutes a day for physical exercise.

    ____A simple 9-minute run around your neighborhood can do wonders for yourself. Exercise can not only help you maintain your regular weight, but also make feel better about yourself.

    Travel and allow yourself to be interested in new people.

    Don't just limit yourself to your fellow travelers-try to connect with the service staff. You never know what kind of people they're going to be. Get out of your house or go online right now to book your class.____

A. You should do it continuously.

B. Someone may hang up on you.

C. You don't need to go to the gym.

D. Running in the gym may be a better choice.

E. Start to travel now and learn to challenge yourself.

F. Take a class for a hobby you've been wanting to develop.

G. You can never see any improvement if you stick to your comfort zone.