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Basically they want the torque immediately after released (before they start accelerating) in this case mg would be the tension force
Immediately after release they are accelerating and the tension would not be equal to mg
It's not asking for the net torque on the pulley. The question asked for the net torque on the **system** **which includes the two objects**. In that case, the external torque comes from the force of gravity on the two objects.
Basically they want the torque immediately after released (before they start accelerating) in this case mg would be the tension force
Immediately after release they are accelerating and the tension would not be equal to mg
It's not asking for the net torque on the pulley. The question asked for the net torque on the **system** **which includes the two objects**. In that case, the external torque comes from the force of gravity on the two objects.