Final answer:
The correct answer is option d) Compression of a spring.
Step-by-step explanation:
When analyzing energy exchanges in a system, we can identify them as primarily involving either heat or work, and we can determine the sign of δE, which represents the change in internal energy of the system.
- a) Expansion of a gas in a cylinder: This involves work performed by the gas as it expands against external pressure. Since the system (gas) does work on its surroundings, the change in internal energy of the system (δE) is negative.
- b) Frictional forces on a moving object: Energy is transferred as heat due to friction. The system loses energy, so δE is negative for the object experiencing friction.
- c) Conduction of heat through a metal rod: Heat is transferred through the rod from a warmer to a cooler area, which is a heat transfer process. The rod itself does not do work, and the direction of δE depends on whether the rod is gaining or losing heat.
- d) Compression of a spring: This involves doing work on the spring to compress it. The system (spring) gains energy, so δE is positive for the spring.
Now considering the energy transfer methods for adding or removing energy from a system, transferring energy through heat or by doing work are the ways in which energy can be added to or removed from a system.