The Foreign Minister said,“ our hope that the two countries will work towards peace.”
A:This is
B:There is
C:That is
D:It is
如图所示,手用F1的力直接将物体B匀速提升h,F1做功为300J;若借助滑轮组把B匀速提升相同高度,滑轮组机械效率是30%,则F2做功为____J.