问题 计算题

汽缸截面积为S,质量为m的梯形活塞上面是水平的,下面倾角为。,如图所示。当活塞上放质量为M的重物而处于静止.设外部大气压为P0,若活塞与缸壁之间无摩擦.求汽缸中气体的压强?

答案

 

取活塞和重物为研究对象,进行受力分析:受重力(m+M)g,活塞受到大气竖直向下的压力P0S,同时也受到封闭气体对活塞的推力P·S’,方向跟活塞斜面垂直,如图所示.同时右缸壁对活塞有弹力N作用,方向水平向左,它们处于平衡状态,符合共点力平衡的条件,即合力等于零.

所以在数值上(m+M)g+ P0S 与N的合力等于PS’,且反向.

又∵

阅读理解

阅读理解。

                                                                   Potato Chips

        History: Potatoes came from South America. We know that the people of Peru were eating potatoes

as long as 2,000 years ago.

        Potatoes were not widely grown in Europe (欧洲) until the early 19th century.

        Production: The first chip factory in Britain was opened in the early 1900s by Frank Smith. For about

50 years, Smith's Chips were the only ones that you could buy. Potatoes are cut, cooked in vegetable oil

(油), dried and packed. It takes only 12 minutes to turn a potato into a bag of chips. 

       Chips are the most popular snack (零食) in the UK. Around 8,500 million bags are sold every year.

Each person eats 3.5 kg every year.

       Making potato chips in South America 

       Potatoes are grown in the mountains of South America. This is how the village people make their own

potato chips.

A. At harvest (收获) time, the villagers dig up the potatoes and bring them into the village. The potatoes are

     put on the ground in the middle of the village.

B. The villagers walk all over the potatoes and flatten (弄平) them. They do this every day and keep on doing

     so for five days.

C. While they are out in the open, the potatoes are dried in the sun and in the cold night air, the potatoes are

     left on the ground.

D. After five days, the chips are ready and are put into strong bags. The potato chips are kept in the food

     store until winter.

     After reading the steps above in making potato chips, please match them to the pictures below.

( )1.

( )2.

( )3.

( )4.

选择题