The first law of thermodynamics generalizes the concept of energyconservation to include heat energy. you probably alreadyappreciate that loss of total mechanical energy (e. g., fromnonconservative forces such as friction) does not destroy energy, but rather converts mechanical energy into heat. this process canbe described quantitatively by the first law of thermodynamics.
by relating heat, internal energy, and work, the first law laysthe groundwork for thermodynamics, a field that also explains theconversion of heat into mechanical energy.

like the law of mechanical energy conservation that itgeneralizes, the first law of thermodynamics relates thechanges in energy that occur from the beginning to the endof some process. the first law of thermodynamics involves changesin the following physical quantities:

w: work done by the system on theoutside world,
q: heat added to the system by theoutside world, and
deltau: internal energy change ofthe system.
you need to look carefully at the wording used here; some otherdisciplines (such as chemistry) use a different sign convention forw.

a) which of the following is the signconvention that results from these definitions?

w is positive when the system is compressed, andq is positive when heat is added to thesystem.
w is positive when the system expands, andq is positive when heat is added to thesystem.
w is positive when the system is compressed, andq is positive when heat is taken from thesystem.
w is positive when the system expands, andq is positive when heat is taken from thesystem.