Work-Energy Principle (Practice Problems)
On this page you can practice solving dynamics problems using the Work-Energy Principle. I urge you to work out the problem first, or try to. Then you can use the attached videos to test your understanding.
Table of Links
Ramp and Belt Problem
A problem with a frictionless ramp and a belt with friction.
Ramp and Spring Problem
Here’s a problem that has friction, gravity, and a spring.
Before watching this video you should try to work out the problem on your own.
The Box Bumper Problem
Another version of a classic work-energy problem:
A solution is posted here. For comparison, I have also worked out a solution using Newton’s Second Law here. (Not for the feint of heart.)
Work-Energy vs. F=ma
When should we use the Work-Energy Principle and when should we use F = ma? Usually work-energy is simpler to use, but it’s not always possible to use it. Being able to identify which problems make good candidates for work-energy is an valuable skill to have. As illustrated in the video below, here are some good rules of thumb.
You may be able to use the Work-Energy Principle if:
- Work is relatively easy to calculate (e.g. Spring forces, gravity, constant forces).
- The problem does not involve time.