1. The problem statement, all variables and given/known data prove that when the net force on a rigid body is zero, the torque about any line perpendicular to the plane of the forces is equal. 2. Relevant equations [tex]\tau[/tex]=I[tex]\alpha[/tex] 3. The attempt at a solution it is known that angular velocity, and hence angular acceleration about any line is the same for a given rotating rigid body. implies, [tex]\alpha[/tex] is same about all lines. if we accept the above statement to be true, then I comes out to be equal about every axis, which is a contradiction.