已知 . F 1 = . i +2 . j +3 . k , . F 2 =-2 . i +3 . j - . k , . F 3 =3 . i -4 . j +5 . k ,其中 . i , . j , . k 为单位正交基底,若 F 1 , . F 2 , F 3 共同作用在一个物体上,使物体从点M 1 (1,-2,1)移到M 2 (3,1,2),则这三个合力所作的功为( )
【简答题】听对话,回答问题。 1. How much does Mike like traveling? A. He enjoys traveling. B. He doesn't like traveling. C. He enjoys working in the space museum. 2. Who do you think Peter is? A. Lily's husband. B. Lily...