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Home Minds On Work and Energy Mission WE9 Work and Energy Conversions Help Help 4

Mission WE9 Work and Energy Conversions

The Question

Consider the work energy bar charts shown below. Type the letter of any bar chart that portrays a situation in which mechanical energy is NOT conserved.

Dig that Diagram

The bar charts depict the form of energy present in the initial and final state and depict how this energy changes (if it does). The height of each bar is representative of the amount of that form of energy. The bar charts also depict the non-conservative work that is done as the object moves from its initial to final state. This work can be positive or negative, depending on whether the bar extends above zero or below zero.

Physics Rules

Work - Mechanical Energy Relationships:
If non-conservative forces do net work upon an object, then the total mechanical energy of that object is changed. The sum of the kinetic and potential energies will change as work is done upon the object.

Think About It

There are two effective approaches to this question. First, add the heights of the kinetic energy (K) and potential energy (P) energy bars for both the initial and the final state. If there is a difference in the sum of the heights (representing the total mechanical energy), then you can conclude that mechanical energy is not conserved for that situation. The easier approach might be to simply observe the bar labeled W for non-conservative work. If there is any non-conservative work being done in any situation, then you can conclude that mechanical energy is not conserved for that situation.

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