A motor does 30 kJ of work and gains 4 kJ as heatfrom the surroundings. What is the change in the internal energy of the motor?

Internal energy ∆U=-26KJ

Explanation:

Given that:

Work done by the motor=+30KJ

Heat gained by the motor=+4KJ

In solving thermodynamical questions it is reasonable to use the sign convention this

Heat is positive if it is added to a system, but becomes negative if the system rejects heats.

Work is positive if the system does work, but becomes negative if work is done on the system.

Using the thermodynamics first law

∆U=Q-W

∆U = 4-30=-26KJ