Final answer:
The change in internal energy of the system that receives 1240 J of energy as heat and does 960 J of work is 280 J, according to the first law of thermodynamics.
Step-by-step explanation:
To determine the change in internal energy of the system, we can use the first law of thermodynamics, which states that the change in internal energy (ΔU) of a system is equal to the heat (Q) added to the system minus the work (W) done by the system.
ΔU = Q - W
In this scenario, the system receives 1240 J of energy as heat (Q=1240 J) and does 960 J of work (W=960 J), so applying the formula:
ΔU = 1240 J - 960 J
ΔU = 280 J
Therefore, the change in internal energy of the system is 280 J.