6. It is clear that the whole world is passing through a social revolution in which a central _____ must be taken by scientists and technologists.

　 A. process　　 B. attention　　 C. measure　　 D. part

5. When I took his temperature, it was two degrees above _____.

　 A. average　　 B. ordinary　　 C. regular　　 D. normal

4. Even if they are on sale, these refrigerators are equal in price to, if not more expensive than, _____ at the other store.

　 A. anyone　　 B. the others　　 C. that　　 D. the ones

3. His landlady gave him a week's _____ to leave the flat.

　 A. threat　　 B. notice　　 C. advice　　 D. caution

2. The noise was so _____ that only those with excellent hearing were aware of it.

　 A. dim　　 B. soft　 　C. faint　　 D. gentle

1. We can't _____ one to change the habits of a lifetime in a short time.

　 A. hope　　 B. wait　　 C. expect　　 D. imagine

23．(10分)如图所示，一个放置在水平地面上的木块，其质量为m=2kg，受到一个斜向下的、与水平方向成37^o角的推力F=10N的作用，使木块从静止开始运动，运动2.4m的距离后撤去推力，若木块与地面间的动摩擦因数μ=0.1。求：(已知sin37⁰=0.6，cos37⁰=0.8，)

(1)撤去推力F瞬间，物体的动能。

(2)撤去推力F后4s内，物体的位移。(g=10m/s²)

22．(10分)如图所示，半径R=2m的四分之一粗糙圆弧轨道AB置于竖直平面内，轨道的B端切线水平，且距水平地面高度为h=1.25m，现将一质量m=0.2kg的小滑块从A点由静止释放，滑块沿圆弧轨道运动至B点以v=5m/s的速度水平飞出(g取10m／s²)．求：

(1)小滑块沿圆弧轨道运动过程中所受摩擦力做的功；

(2)小滑块经过B点时对圆轨道的压力大小；

(3)小滑块着地时的速度大小。

21. (8分)一个人在某一星球上以速度竖直上抛一个物体，经时间落回抛出点。已知该星球的半径为，求该星球的第一宇宙速度。

20．(8分)用细绳AC和BC吊起一重物，两绳与竖直方向的夹角如图所示， AC能承受的最大拉力为150 N，BC能承受的最大拉力为100 N。为使绳子不断裂，所吊重物的质量不得超过多少? (g=10m/s²)