Читать книгу Physics I For Dummies - Steven Holzner - Страница 73

There you are, getting into your Physics racer as the crowd cheers. It’s time for some hefty acceleration. You get out your clipboard. What acceleration would you need to end up at 100 miles per hour at the end of a 1.0-mile racetrack?

Okay, you think. You need an equation that relates speed, acceleration, and displacement. It’s time for

In this case, it’s even a little easier, because you know that the initial velocity is 0 , so you have

Well, well, it looks like the problem is half-solved. Putting in the numbers gives you

Now solve for a:

Miles per hour²? What the heck kind of units are those? Change that to something more understandable, such as mph per second. To change one of the per-hour units to per-second, multiply by the conversion factor (see Chapter 2):

So your velocity would be increasing by only 1.4 mph every second — that’s not too outrageous — you’d feel a mild acceleration, that’s all.