题目

图1为测量物块与水平桌面之间动摩擦因数的实验装置示意图．实验步骤如下：①用天平测量物块和遮光片的总质量M、重物的质量m；用游标卡尺测量遮光片的宽度d；用米尺测量两光电门之间的距离s；②调整轻滑轮，使细线水平；③让物块从光电门A的左侧由静止释放，用数字毫秒计分别测出遮光片经过光电门A和光电门B所用的时间△tA和△tB ， 求出加速度a；④多次重复步骤③，求a的平均值 ；⑤根据上述实验数据求出动摩擦因数μ．回答下列问题： Penguins are birds，but they can’t fly．They can stand and walk．It’s very interesting to see penguins walking．When they walk，they sway（摇摆）their bodies．It makes them look cute and funny．     Penguins are short and fat。but not very heavy．With black backs and white bellies（腹部），they look like gentlemen wearing tailcoats．     Penguins live in cold places so they must eat a lot every day．Fish are their favorites．They are small．but they can eat a lot of fish．     I like penguins very much．Penguins are always friendly．They are not afraid of（害怕）meeting people．They like to make friends with us．Do you like penguins, too? 根据短文内容，判断下列句子正误。正确的用“A”表示，不正确的用“B”表示。 1．Penguins are fish. 2．When they walk they sway their bodies. 3．Penguins are short and heavy. 4．Penguins are small, so they eat a little fish. 5．Penguins are afraid of seeing people.