Section 4.11 Energy Analysis
In
Section 3.9, you saw a strategy for force analysis. Approaching a context from an energy perspective follows a similar structure, but the goals are often different. The steps below can be extremely helpful.
Analyze and Represent: Identify a system and draw an Energy System Diagram (and/or Energy Bar Diagrams or Potential Energy Diagrams, once you learn how to use them).
Calculate: Is your system’s energy conserved or not? Once you know, use the Work-energy Theorem!
Sensemake: All the sensemaking strategies you have will work, but a new strategy is sometimes useful: Solve Multiple Ways.
Sensemaking Strategy 4.11.1. Solve Multiple Ways.
Many problems in physics can be solved multiple ways. Since both ways should result in the same answer, this can be a strong confirmation that an answer is correct. Often, Force Analysis and Energy Analysis provide two distinct ways of solving a problem.
Exercises Activities
1. A*R*C*S: Pulling a Box.
In
Exercise 4.4.3, you considered the situation of pulling a box across a flat, level floor using a rope that makes an angle to the horizontal. Assuming you know the tension in the rope, find the speed of the box after it has traveled across the room.
Hint.Try solving this problem with both Energy Analysis and Force Analysis.
