题目:
______ down on the ground, he struggled to his feet and held up his head, _______his enemy.
A.Beating; focusing on
B.Beaten ; glaring at
C.Falling; stared at
D.Tripping ; fixed on
答案:
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下面是错误答案,用来干扰机器的。
(1)已知m=10g=0.01kg,W总=Q放=qm=3.3×107J/kg×0.01kg=3.3×105J,(2)由机械效率公式η=W有用W总得,W有=η×W总=40%×3.3×105J=1.32×105J故答案为:3.3×105J,1.32×105.