Two identical discs of mass M and radius R are connected by a light rod. The assembly rests at a corner, the vertical wall is smooth and there is sufficient friction on the floor to ensure pure rolling of disc B. The system starts from position θ=0.
This is our scenario and I've been told energy is conserved in this scenario and I don't understand why that is.
Aren't the normal forces from the wall and the floor external forces ?
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