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### Unit Conversions: mph to fps

```Date: 03/06/2003 at 19:51:58
From: John
Subject: Converting miles per hour to feet per second

How can I find out how many feet per second I could travel driving 55
miles per hour?
```

```
Date: 03/06/2003 at 23:33:53
From: Doctor Jeremiah
Subject: Re: Converting miles per hour to feet per second

Hi John,

You thought fractions would never be good for anything!

Forget the numbers and concentrate on the units:

55 miles
--------
1 hour

What would you multiply this by to cancel the hours?

55 miles   hours   miles
-------- x ----- = -----
1 hour     sec     sec

What is hours/second? There are 3600 seconds in 1 hour so
hours/second = 1 hour/3600 seconds which means:

55 miles   1 hour     55 miles
-------- x -------- = --------
1 hour    3600 sec   3600 sec

Now, what would you multiply miles/sec by to get feet/sec?

55 miles   feet   feet
-------- x ---- = ----
3600 sec   mile    sec

What is feet/mile? There are 5280 feet in 1 mile so
feet/mile = 5280 feet/1 mile which means:

55 miles   5280 feet   55 x 5280 feet
-------- x --------- = --------------
3600 sec      1 mile      3600 sec

This works for any conversion. You just multiply the fractions that
are appropriate and you end up with the answer.

In this particular instance, as a check, you can use the fact that
60 miles per hour is the same as 88 feet per second.

- Doctor Jeremiah, The Math Forum
http://mathforum.org/dr.math/
```
Associated Topics:
Elementary Fractions
Elementary Measurement

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