A horizontal torque=10.0 Nm is applied at the edge of the top face of a hollow cylindrical rod. The base of the rod is fixed to the surface. The outer radius of the cylinder is ro=0.040 m and the inner radius is ri =0.020 m. The shear modulus of the material used to produce the rod is 3.0 x 10^7 N/m^2 . If the hollow rod twists by an angle of 0.250 rad what is the length of the cylinder in m