Question

is work done when lady is cooking food?

Answer 1

let us assume that the lady is stirring her hand while cooking. In order to do this she has to consume the energy in her. If we take the lady as the system she has done work as the stirring action mixes the food. Since this takes place in a situation where pressure and volume is kept constant(ideal situation). Hence, heat dissipation takes place. So we can say that the internal force of the lady (muscular forces) did some work to dissipate the energy (heat) of the vessel in which food is being cooked. So in this case, work is done by the lady as her internal forces are non conservative in nature. But if we take the room in which the lady is cooking and describe it as the system and examines whether she works or not, the answer is no. As then, all the forces would be considered as internal forces and thus the system wouldn't do any work. The only visible change here would be that the potential energy of the system increases as the internal forces are non conservative in nature.

So, it all depends on what you define the system.