# 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*.