Final answer:
In physics, the system is the shopping cart and its interactions, where a push represents mechanical energy transferred to the cart. This energy is partially converted to kinetic energy, propelling the cart, and partially lost as heat due to friction, demonstrating the first law of thermodynamics.
Step-by-step explanation:
A physicist would define the system as the shopping cart and anything inside it, as well as the interacting forces. In analyzing its motion, they would consider how a push (mechanical energy) moves the cart, focusing on the kinetic and potential energy changes. When pushing the shopping cart, work is done on the system, which increases its energy—mainly in kinetic form if it accelerates, or in maintaining motion against friction. Meanwhile, some energy transfers occur due to friction between the cart and floor, where mechanical energy is converted into heat, exemplifying a loss of usable energy from the system. This process of energy loss aligns with the first law of thermodynamics, which implies that in a closed system, like our shopping cart system, energy is conserved but can change forms.