Читать книгу Physics I For Dummies - Steven Holzner - Страница 71

Given initial velocity, time, and acceleration, you can find displacement. Here’s an example: There you are, the Tour de France hero, ready to give a demonstration of your bicycling skills. There will be a time trial of 8.0 seconds. Your initial speed is 6.0 meters/second, and when the whistle blows, you accelerate at 2.0 m/s² for the 8.0 seconds allowed. At the end of the time trial, how far will you have traveled?

You could use the relation , except you don’t start off from zero speed — you’re already moving, so you should use the following:

In this case, , , and , so you get the following:

You write the answer to two significant digits — 110 meters — because you know the time only to two significant digits (see Chapter 2 for info on rounding). In other words, you ride to victory in about 110 meters in 8.0 seconds. The crowd roars.