解:F1=man=m lsin e mg+f+F=o ∑∑ Fh=0, F cos0-mg=0 F=0.F sin0-F=0 解得 mg =1.96N cos 0 frisina =2.lm /s解: 2 sin n I n v F ma m l  = = mg + FT + FI = 0    0, cos 0 Fb = F1  − mg =  = 0, sin − = 0 n F n FT  FI 解得 1.96N cos = =  mg FT s sin 2.1 m 2 = = m F l v T 