问题 多选题

在水平面上运动的物体,从t=0时刻起受到一个水平力F的作用,力F和此后物体的速度v随时问t的变化图象如图甲、乙所示,则(  ) 

A.在t=0时刻之前物体所受的合外力一定做负功

B.从t=0时刻开始的前3s内,力F做的功为零

C.除力F外,其他外力在第1s内做正功

D.力F在第3s内做的功是第2s内做功的3倍

答案

A、因为在t=0时刻开始受到水平拉力F,做匀速直线运动,知物体在0时刻之前受到的合力与F拉力方向相反,知在t=0时刻之前,合外力做负功.故A正确.

B、从t=0时刻开始前3s内,动能变化为零,则合力做功为零,摩擦力做功不为零,则力F做功不为零.故B错误.

C、在第1s内,做匀速直线运动,合力做功为零,则除力F以外,其它外力做负功.故C错误.

D、根据速度时间图线知,第2s内和第3s内的位移相等,拉力大小之比为1:3,所以力F在第3s内做的功是第2s内做功的3倍.故D正确.

故选AD.

阅读理解

There’s a body of water in Israel that is actually below sea level. Water constantly runs into it, but, because of the law of gravity (万有引力定律),nothing can flow out of it. Do you know the name of this famous lake? It’s called the Dead Sea. It’s called this because no living thing could live there. The water is almost dead, compared to what happens with “living water”.

When you think of the term “living water”, the image that comes to mind is a rushing river that is flowing. It’s filled with life and movement. It doesn’t just “receive”, but is also “giving” simultaneously.

Many of us believe that we need to receive more of something in order to be happy. Whether what we desire is money or something else, we think we need more of it in order to be fulfilled.

As a result, we begin to operate in fear and therefore don’t give anything because we’re afraid that we won’t have enough. The result? Like the Dead Sea, we become lifeless. Life is meant to flow. when a pool stops flowing, it becomes stagnant(停滞的). Stagnant water breeds disease and death. It can’t breathe. It can’t receive any more. If nothing is flowing out, there’s no room for anything else to come in.

The solution? Give. As you give, you’ll receive. It’s a universal law. You see it at work everywhere. we’ve somehow been deceived ( 欺骗 )into believing that if we don’t give, we’ll have more. Or we’re afraid that if we do give, we won’t have anything left. On one hand, this seems to make sense. But it doesn’t work. Because when we don’t give, we shut off the flow of what’s coming in.

小题1:What is the first paragraph mainly about?

A.The development of the Dead Sea

B.The special character of the Dead Sea

C.The position of the Dead Sea

D.The present situation of the Dead Sea小题2:According to the passage, people wouldn’t like to give because________.

A.they are really poor in fact

B.they don’t know how to give

C.they don’t know who to give

D.they are still not satisfied小题3:According to the passage, if you refuse to give, you will___________.

A.be like a pool with stagnant water

B.have enough space for what you’ll receive

C.need something more to be satisfied

D.do everything according to the law小题4:What would be the best title for the passage?

A.Give and you’ll receive

B.The secret of the Dead sea

C.A universal law

D.come in and come out

单项选择题