Finding Miles Per HourDate: 03/06/2002 at 20:21:44 From: joshua Subject: RPM (How to find mph) Let's say I'm going 64.2 rpm. How many mph am I going? How do you solve it? Date: 03/06/2002 at 21:26:21 From: Doctor Twe Subject: Re: RPM (How to find mph) Hi Joshua - thanks for writing to Dr. Math. That depends on the size of your wheel(s). Suppose your tire is 28" in diameter. Then the circumference is 28*pi inches, or about 88". Assuming that there is no slippage, that means that the wheel is moving 88" every time it makes one complete revolution. At 60 rpm, that equals 60 * 88" = 5280" every minute. Now we must convert inches per minute to miles per hour. There are 60 minutes per hour so: 5280 in. 60 min. 316,800 in. -------- * ------- = ----------- 1 min. 1 hr. 1 hr. There are 12 inches per foot, so: 316,800 in. 1 ft. 26,400 ft. ----------- * ------ = ---------- 1 hr. 12 in. 1 hr. And finally, there are 5280 feet per mile, so: 26,400 ft. 1 mi. 5 mi. ---------- * -------- = ----- 1 hr. 5280 ft. 1 hr. So with a 26" diameter wheel (and no slippage), 60 rpm = 5 mph. I hope this helps. If you have any more questions, write back. - Doctor TWE, The Math Forum http://mathforum.com/dr.math/ |
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