14. Jim does well in aid climbing. He wants to challenge his courage in the extreme sports,
and climbing can give him a wonderful view of nature.
13. Jane is fond of wild creatures. She thinks it is not wise to keep the animals in the cage.
How she wishes she could get close to nature while she is watching the animals!
12. Translate the underlined sentence in the last paragraph into Chinese.
__________________________________________________________________________
C
A
Whenever there’s a coral reef, the chances are there are divers nearby. Diving is one of the fastest-growing water sports in the world. Among the world’s favorite diving sports are the northern edge of Australia’s Great Barrier Reef and the Maldives’ islands in the Indian Ocean. There, there is enough underwater activity to satisfy the most demanding diver.
B
People have been skiing since 3000 BC, but the birth of modern skiing --- for pleasure rather than necessity --- only began in the late 19th century. Since then, winter’s top sport has become an industry. European countries, especially those along the Alps are famous for their skiing spots. Norway, France and Switzerland are good choices. There you can enjoy plenty of exercise among the mountainous forests while breathing in the fresh air. Within a couple of lessons, you will be gliding through the trees in style.
Many beautiful mountains are now linked by steel cables and ladders. You can work your way up the kind of rocks that would otherwise be only fit for birds. Besides the proper equipment, you often need a strong will. Europe’s highest mountain, Mont Blanc at 4807 meters, is a common goal for climbers worldwide.
D
Have you been to Shanghai? Did you climb the TV tower? The tower is the highest in Asia, and the CN Tower is in Toronto. Let’s view the city from the tower. Most buildings in Toronto are not very high. But the CN tower stands out among the buildings. It is 553 meters high, the world’s highest tower.
E
In a zoo without bars, safaris are adventure in its purest form. Out on safari, it is the animals who rule the land. From jeeps, you can see the struggles of life and death in a variety of wildlife, such as elephants, lions, birds and snakes.
The national parks in Africa are the perfect places for safaris.
F
At first it all seems rather easy as you drift along with the water only occasionally reaching over the sides of your raft. And then suddenly, you realize why they call it white-water rafting.
First comes the dull, distant roar of rapids, then a wash of white water and finally the roller-coaster ride that turns you at top speed down the river. The Bio-Bio River in Chile and the Colorado River in the US are among the finest white-water destinations.
11. Which is the better way to see the sights in Manhattan---to take a bus or to walk? Why?
10. Please fill in the blank in the second paragraph with proper words and phrases to complete the sentence. (Please answer within 10 words)
9. Which sentence in the passage can be replaced by the following one?
A street known as the Fifth Avenue divides Manhattan into two parts---the east and the west.
8. What is the best title of the passage? (Please answer within 10 words.)
11.
图3－2－19
如图3－2－19所示，长L＝1.5 m，高h＝0.45 m，质量M＝10 kg的长方体木箱，在水平面上向右做直线运动．当木箱的速度v0＝3.6 m/s时，对木箱施加一个方向水平向左的恒力F＝50 N，并同时将一个质量m＝1 kg的小球轻放在距木箱右端的P点(小球可视为质点，放在P点时相对于地面的速度为零)，经过一段时间，小球脱离木箱落到地面．木箱与地面的动摩擦因数为0.2，其他摩擦均不计．取g＝10 m/s2.求：
(1)小球从离开木箱开始至落到地面所用的时间；
(2)小球放在P点后，木箱向右运动的最大位移；
(3)小球离开木箱时木箱的速度．
解析：(1)小球从离开木箱开始至落到地面所用的时间
由h＝gt2，t＝ ＝ s＝0.3 s.
(2)小球放到木箱上后相对地面静止，木箱的加速度为
a1＝＝ m/s2＝7.2 m/s2
木箱向右运动的最大位移为：x1＝＝ m＝0.9 m.
(3)x1小于1 m，所以小球不会从木箱的左端掉下．
木箱向左运动的加速度为a2＝＝ m/s2＝2.8 m/s2
设木箱向左运动的距离为x2时，小球脱离木箱x2＝x1+＝0.9 m+0.5 m＝1.4 m
设木箱向左运动的时间为t2，由x＝at2得t2＝ ＝ s＝1 s
小球刚离开木箱瞬间，木箱的速度方向向左，大小为v2＝a2t2＝2.8×1 m/s＝2.8 m/s.
答案：(1)0.3 s (2)0.9 m (3)2.8 m/s
10.
图3－2－18
如图3－2－18为一滑梯的示意图，滑梯的长度AB为L＝5.0 m，倾角θ＝37°.BC段为与滑梯平滑连接的水平地面．一个小孩从滑梯顶端由静止开始滑下，离开B点后在地面上滑行了s＝2.25 m后停下．小孩与滑梯间的动摩擦因数为μ＝0.3.不计空气阻力．取g＝10 m/s2.已知sin 37°＝0.6，cos 37°＝0.8.求：
(1)小孩沿滑梯下滑时的加速度a的大小；
(2)小孩滑到滑梯底端B时的速度v的大小；
(3)小孩与地面间的动摩擦因数μ′.
解析：(1)小孩受力如右图所示
由牛顿运动定律得mgsin θ－μFN＝ma，FN－mgcos θ＝0
解得a＝gsin θ－μgcos θ＝3.6 m/s2.
(2)由v2＝2aL，求出v＝6 m/s.
(3)由匀变速直线运动规律得0－v2＝2a′s，由牛顿第二定律得μ′mg＝ma′，解得μ′＝0.8.
答案：(1)3.6 m/s2 (2)6 m/s (3)0.8
9.
图3－2－17
两个完全相同的物块A、B，质量均为m＝0.8 kg，在同一粗糙水平面上以相同的初速度从同一位置开始运动．图3－2－17中的两条直线分别表示A物块受到水平拉力F作用和B物块不受拉力作用的v－t图象，求：
(1)物块A所受拉力F的大小；
(2)8 s末物块A、B之间的距离x.
解析：(1)设A、B两物块的加速度分别为a1、a2，
由v－t图象可得：
a1＝＝ m/s2＝0.75 m/s2①
a2＝＝ m/s2＝－1.5 m/s2
负号表示加速度方向与初速度方向相反．②
对A、B两物块分别由牛顿第二定律得：
F－Ff＝ma1③
－Ff＝ma2④
由①-④式可得：F＝1.8 N.
(2)设A、B两物块8 s内的位移分别为x1、x2由图象得：
x1＝×(6+12)×8＝72 m，x2＝×6×4＝12 m，所以x＝x1－x2＝60 m.
答案：(1)1.8 N (2)60 m
