Question

Give a specific example of a system with the energy transformation W→U. In this question W is the work done on the system by the environment, and K and U are the kinetic and potential energies of the system, respectively. Any energy not mentioned in the transformation is assumed to remain constant; if work is not mentioned, it is assumed to be zero. Select a specific example of a system with the energy transformation shown.

K→ΔEth

Select a specific example of a system with the energy transformation shown.

A. A wood block sliding across a rough horizontal surface and slowing to a stop.

B. A block sliding on level ground, to which a cord you are holding on to is attached

C. A wood block moving across a horizontal rough surface at constant speed

D. A wood block sliding down a rough inclined surface at a constant speed.

Answer 1

A spring being compressed exemplifies W→U (work transforming into potential energy), while a wood block sliding to a stop due to friction represents K→ΔEth (kinetic energy transforming into thermal energy). Heat transfer Q and work done W are transient forms of energy, while internal energy U is stored within a system.

Step-by-step explanation:

To answer the first part of your question: a specific example of a system with the energy transformation W→U (work done on the system resulting in an increase of internal energy) could be compressing a spring. Work done on the spring is stored as potential elastic energy in the spring system.

Regarding the second part of your question which deals with K→ΔEth (kinetic energy transforming into thermal energy), the correct answer is A. A wood block sliding across a rough horizontal surface and slowing to a stop. In this example, friction does work on the wood block, converting its kinetic energy into thermal energy which increases the temperature of both surfaces.

Heat transfer Q and work done W are always energies in transit, while internal energy U is energy stored within a system. An example of heat transfer could be a hot cup of coffee cooling down to room temperature; this represents heat leaving the cup as it transfers to the surrounding air. Work done could be pushing a book across a table; the energy used in the action is transferred to the book as kinetic energy. Internal energy, such as in food, represents stored molecular potential energy, which can be converted into kinetic energy in our bodies.

Answer 2

Option A

Step-by-step explanation:

When a wood block slides across a rough horizontal surface and slows to a stop, kinetic energy is converted to thermal energy because as it moves, the velocity decreases in the motion which results in loss of kinetic energy. From the principles of conservation of energy, the kinetic energy will be converted into thermal energy.