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【单选题】
作用于手柄端的力F =800 N，
试计算力F在y轴上的投影为（ ）。
A.
-282.8N
B.
282.8N
C.
400N
D.
-400N
参考答案：
参考解析：
刷刷题刷刷变学霸
举一反三
【单选题】After the birth of my second child，I got a job at a restaurant.Having worked with an experienced 16for a few days，I was 17to wait tables on my own.All went 18that first week.When Saturday night came，I...
A.
repeated
B.
discovered
C.
corrected
D.
described