CH12.Problems

JH.131

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!

-Ta + Tc cos30 = 0

Tc Sin30 -240 = 0

Only forces no torques

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

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