Newtons Law for rotation says that the net torque on a rigid body about some axis equals its moment of inertia times its angular acceleration:
   
    tnet = I * a

where tnet is the net torque vector, I is the moment of inerta of the body,  and a  is its angular acceleration vector.
In Andes problems, torque and angular acceleration vectors lie entirely along the z axis, so this vector principle may be applied in component form as

    tnet_z = I * a_z

This principle is the rotational counterpart of Newton's Second Law Fnet = m * a.