Determining the height of a building with a stopwatch

This is the first video in our homework problem solution series. It is a classic example of a one-dimensional motion problem most students would encounter in an introductory physics class.

The problem: I go outside and climb onto the roof of the building. I drop a rock off of the top and with a stopwatch I time how long the rock takes to reach the ground. The stopwatch reads 2 seconds when the rock hits the ground. How tall is the building?

Click on the video below to see the solution worked out in real time. The text in the video is impossible to read, but it is just the problem above written out. Future videos will have this problem corrected. The actual problem solving is clear.

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