1. CH12.Problems JH.131

7. Take the lower center as rotation center then: M2 (L/4) = M3 (3L/4)  M2= 3 M3 Now the upper center: M1 (L/4) = (M2+M3) (3 L/4)  M1 = 3(M2+M3) = 3* 4 = 12kg  Only Torques, no forces!

8. -Ta + Tc cos30 = 0 Tc Sin30 -240 = 0 Only forces no torques

9. Project! Mg (L/2 sin alpha) is cw torque 2Mg (L) Sin(90-alpha) is CCW torque Then 2 Cos(alpha) = Sin(alpha) /2 Or Tan (alpha) = 4  alpha = 76 deg

13. Any triangle =180; so, beam makes 60 with vertical