沂蒙山区有一首民谣:板凳鏊子三十三,一百个爪儿地上安.板凳鏊子各多少?你可以算出来吗?（板凳4个爪,鏊子3个爪,爪即“腿

解题思路：知道氧气瓶的体积，可以知道氧气瓶浸没在水中排开水的体积，根据阿基米德原理求氧气瓶受到的浮力；知道氧气瓶和里面氧气的质量，利用重力公式求总重；要有助于上浮，氧气瓶受到的浮力必须大于自重，可求用去氧气的重，再利用重力公式求用去氧气的质量．

氧气瓶浸没在水中受到的浮力：
F_浮=ρ_水gv_排=1.0×10³kg/m³×10N/kg×7.5×10^-3m³=75N，
氧气瓶总重：
G_总=（m_瓶+m_气）g=（6kg+3kg）×1ON/kg=90N，
有助于上浮至少用去的氧气的重：
G=G_总-F_浮=90N-75N=15N，
m=[G/g]=[15N/10N/kg]=1.5kg
答：至少用去1.5kg氧气后，氧气瓶才有助于潜水员上浮．

点评：
本题考点： 物体的浮沉条件及其应用；重力的计算；阿基米德原理．

考点点评： 本题的研究对象是氧气瓶及里面的氧气，能正确对它做出受力分析是本题的关键．

翻译：
being well known as yimeng mountain area,the city linyi is located in south eastren of shandong province,extremely beautiful with the mountains and rivers,though the euphonious yimeng tunes,you can see the whole beautiful sceneries of yimeng.
资料：
Linyi (simplified Chinese:临沂; traditional Chinese:临沂; pinyin:Línyí) is a prefecture-level city in the south of Shandong province,People's Republic of China.The largest prefecture-level city in Shandong,Linyi borders Rizhao to the east,Weifang to the northeast,Zibo to the north,Tai'an to the northwest,Jining to the west,Zaozhuang to the southwest,and the province of Jiangsu to the south.It is twinned with Patras,Greece.
Linyi is about 2400 years old.In the 1970s Sun Tzu's Art of War was unearthed here.
In the spring of 1938,during the Second Sino-Japanese War,the city was the scene of fierce fighting between Chinese and Japanese troops.The Chinese,encouraged by the success of their military in the nearby Battle of Tai'erzhuang,defended Linyi fiercely,but Japanese soldiers breached the walls on April 19,1938.The defenders withdrew the next day to another contested area 30 miles away.
After the People's Republic of China was founded in October 1949,the administrative division was adjusted.
[edit] Geography and climate
Linyi enjoys a temperate climate and high precipitation.The lie of the land varies,with mountains,hills,and plains accounting for approximately equal parts of the total area.The entire jurisdiction covers 17,184 km² and the total population is close to 10 million,making this the largest administrative division in the province in both geographic and demographic terms.
[edit] Economy
Linyi's economy is based around its wholesale markets 1.The Linyi Wholesale City is ranked 3rd in its category in China with an annual trade volume of 40 billion RMB US$5 billion).The Linyi prefecture has developed more than 1,500 specialized villages,over 80 specialized towns and nearly 800 industrialized agricultural enterprises.
In 2002 the prefecture's GDP was 71 billion RMB US$16 billion) comprising 12 billion RMB from primary industry,34 billion RMB from secondary industry and 25 billion RMB from tertiary industry.Main industrial products are:textiles,foodstuffs,machinery,electronics,chemicals,building materials,coal,medicines,gold and porcelain.
In 2003 there were 77 enterprises with a pre-tax profit above 10 million RMB (US$1.25 million) and 7 enterprises with a pre-tax profit above 100 million RMB (US$12.5 million).
Machinery is exported to Europe,the Americas and south-east Asia.Linyi prefecture has an annual capacity of 3 million tons of compound fertilizers.
[edit] Notable people
Wang Xizhi (303 - 361 BCE),Eastern Jin Dynasty calligrapher
Zhuge Liang (181 - 234 BCE),statesman and strategist
[edit] Cultural Attractions
Linyi's focal point is the People's Square (Renmin Guangchang).It was built in the early 1990's on the site of an old army barracks.It is about 500 metres east-west,and about 300 metres north-south.Underneath it is a shopping centre and entertainment facilities.
Just north of the city centre is a park dedicated to Wang Xizhi.For a small entrance fee tourists can enjoy a pleasant walk and try Chinese calligraphy.
Near the centre of Linyi city is a museum which houses some original bamboo strips from the Sun Tzu era.