题目

如图，一质量为m的正方体物块置于风洞内的水平面上，其一面与风速垂直，当风速为v0时刚好能推动该物块。已知风对物块的推力F正比于Sv2，其中v为风速、S为物块迎风面积。当风速变为2v0时，刚好能推动用同一材料做成的另一正方体物块，则该物块的质量为( )A. 64m B. 8m C. 32m D. 4m 答案：【答案】A【解析】解：物块被匀速推动，根据平衡条件，有：F=fN=mg其中：F=kSv2=ka2v2f=μN=μmg=μρa3g解得：a=现在风速v变为2倍，故能推动的物块边长为原来的4倍，故体积为原来的64倍，质量为原来的64倍；故选：A句型转换 71. Simon would like two kilos of beef. (对划线部分提问)    How ______ beef ______ Simon like? 72. He does well in playing volleyball. (改为一般疑问句)    _______ he ______ well in playing volleyball. 73.How do you like the fashion show?(同义句转换）    What do you ______ ______ the fashion show? 74.There are some Americans in our school. (改为否定句)    There ______ _______Americans in our school.          75. You look cool in the white T-shirt.(同义句转换)    The white T-shirt ______ cool _______ you.