题目

如图9所示，物块的质量m＝30 kg，细绳一端与物块相连，另一端绕过光滑的轻质定滑轮，当人用100 N的力斜向下拉绳子时，滑轮两侧细绳与水平方向的夹角均为30°，物块在水平面上保持静止，滑轮上端的悬绳竖直(取g＝10 m/s2)．求：   (1)地面对物块的弹力大小和摩擦力大小； (2)滑轮上方竖直悬绳的拉力大小．28、阅读短文，用括号内所给动词的适当形式填空。 You may know the song Happy Birthday very well．But do you know about its writer? It __1__（write）by an American girl．And now she __2__（become）a very rich woman． When she was a child，she was poor．Once she __3__（invite）to her friend's birthday party．She was very pleased but sad because she had not enough money __4__（buy）presents for them． “The party is coming soon．Now I have a little money．” Tears ran down her face．Late that night she was in bed，__5__（think）about the presents when the door opened and in came her grandma．“What happened?” her grandma asked．Hearing the girl’s story，she said，“__6__（not worry）．I think I __7__（help）you．How about __8__（sing）a song together? Happy birthday to．．．” What a beautiful song! They sang and sang．Suddenly she woke up．It was a dream! She decided to write it down at once and sing it to her friends at the party． When she sang the song at the party the next day，he little friends were very happy．“How wonderfully she __9__（sing）! We __10__（not hear）such a song before．Thank you for giving us the special present．” Said one of them．And they learnt to sing it to sing it together．Later the girl became well-known in America． 评卷人 得分 七、书面表达 （每空？ 分，共？ 分）