Answer:
The maximum torque is given by
=2Am*t*r
Were r is the shear stress
Were Am median area =(1-51)^2=2500
Were median line lenght = 4(1-51)=2000
Maximum torque = 2*2500*51*12000=3.06*10^9lbf-in
Corresponding angle of twist©=T*Lm*l/(4*G*Am^2*t)
3.06*10^9*2000*36=2.2*10^12
4*11.5*10^9*2500*10^2*5=1.46*10^19
©=(2.2E12/1.46E19)=1.5E-7rad
Explanation: