问题 选择题

一头牛的质量为400kg,站在水平地面上时,每只脚与地面的接触面积为2×10-2 m2,则牛对地面的压强为:(g=10/kg)(   )

A.2×10PA、                 B.5×10PA、

C.5×10PA、                 D.2×10Pa

答案

答案:D

题目分析:牛的重力G=mg=400kg×10N/kg=4000N,对地面的压力就等于牛的重力,F=G=4000N,

牛对地面的压强

所以选D

点评:本题考查压强的计算,关键知道在水平面上压力等于物体自身的重力,最容易出错的是牛站在水平地面上时与地面的接触面积是四只脚的面积,不是一只脚的面积.

阅读理解

根据短文内容,从短文后的选项中选出能填入空白处的最佳选项.选项中有两项为多余选项.

                                                      Easy Ways to Keep Your Brain Sharp

    Everyone is forgetful, but as we age, we start to feel like our brains are slowing down a bit and

that can be a very annoying thing.__1__    Read on for some techniques worth trying.

1.__2__

     People who regularly made plans and looked forward to upcoming events had a 50 percent

reduced chance of Alzheimer's disease (早老性痴呆症), according to a recent study.__3__    

Something as simple as setting a goal to have a weekly coffee date with a friend will do.There's

evidence that people who have a purpose in life or who are working on long or shortterm goals

appear to do better.In other words, keep your brain looking forward.

2.Go for a walk.

     Mildly raised glucose (葡萄糖) levels can harm the area of the brain that helps you form

memories and physical activity can help get blood glucose down to normal levels.In fact, exercise

produces chemicals that are good for your brain.__4__    

3.Learn something new.

     Take a Spanish class online, join a drawing club, or learn to play cards.A study found that mental

stimulation (刺激) limits the weakening effects of aging on memory and the mind.But the best thing

for your brain is when you learn something new and are physically active at the same time.__5__   

Or go dancing with your friends.

A.Focus on the future.

B.This can be especially harmful to the aged.

C.It should be something like learning gardening.

D.So take a few minutes each day to do some reading.

E.But don't worry if your schedule isn't filled with lifechanging events.

F.Luckily, research shows there is a lot you can do to avoid those moments.

G.In other words, when you take care of your body, you take care of your brain.

问答题 简答题