A motor with an efficiency of 0.80 drives a machine. The machine transfers 60% of the energy it receives usefully. The final useful energy transferred is 960 J. How much energy is dissipated by the motor alone?
640 J640\ \mathrm{J}640 J
240 J240\ \mathrm{J}240 J
400 J400\ \mathrm{J}400 J
1040 J1040\ \mathrm{J}1040 J