Blocks connected via pulley system

Let's talk about problem solving with concepts from Dynamics (Newton's Laws) versus problem solving with concepts from Work, Energy & Power. Many mechanics problems can be fruitfully approached via either the concepts of Dynamics or Work and Energy. Which method do you choose?

With the application of force, the object's motion can be analyzed by looking at the change in the state of motion (velocity) over time (dynamics) or it can be analyzed by looking at the change in the state of motion (kinetic energy) through the application of force over distance (work).

If you find yourself stuck trying to solve a problem with reasoning from Newton's Laws, take a step back and think about the problem in terms of Work & Energy. Often the solution will immediately become clear.

The inclined plane is a classic example. Often the first instinct is to find the acceleration down the plane to determine the final speed, when a simple approach using conservation of energy may be much faster. No method is always best, so if you get stuck using Dynamics, step back and think about Work & Energy.












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