ConversionsDate: Fri, 17 Mar 1995 14:35:24 AST From: Richard Seguin Subject: I have a question like this that I do not know how to do. Nancy ran a distance of 3.8km in 55 min. Calculate her speed. A) Kilometers per hour. B) Metres per second. Date: 5 Apr 1995 15:50:53 -0400 From: Dr. Ken Subject: Re: conversion factors Hello there! I actually didn't learn a good solid way to do these questions until I was in high school, because everyone assumed I already knew how to do them. Here's how I'd approach it. If she ran 3.8 km in 55 minutes, then her speed in km/min. is 3.8 km ------ = .069 km/min. 55 min. To change units, we want to take this figure and multiply it by 1 a whole bunch of times, which won't change the speed. For example, to change the minutes to hours, we know that 1 hour = 60 minutes, so we have 3.8 km 60 min. ------ x ------- 55 min. 1 hour Notice that the minutes in the top and the bottom cancel out. So we're left with 3.8 x 60 km ----------- = 4.1 km/hr. 55 x 1 hours Now see if you can do the second one, noting that 1 km = 1000 m, and 1 minute = 60 seconds. Good luck! -Ken "Dr." Math Date: Fri, 17 Mar 1995 18:39:18 AST From: Richard Seguin Subject: For this Question: In 1956 Australia won the women's 400-m freestyle relay. the race was won in 4 min 17.1s. Calculate the speed in metres per second. My formula would be: V=D 400m - ---- =1.6m/s if I were to round it off. T 257.1s Is this right? Date: 5 Apr 1995 22:12:41 -0400 From: Dr. Ken Subject: Re: conversion factors Yes, that's exactly right! Remember, units of measurement cancel just like everything else does, so when you're done, you can make sure eveything canceled except what you wanted there. Keep it up! -Ken "Dr." Math |
Search the Dr. Math Library: |
[Privacy Policy] [Terms of Use]
Ask Dr. Math^{TM}
© 1994-2015 The Math Forum
http://mathforum.org/dr.math/