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Homework Help: Unit/Metric Conversions

  1. Sep 11, 2007 #1
    Sorry if this is in the wrong forum but I do not know which section this would go into.

    My problem is Im having troubles understanding some of these questions that my teacher had given me.

    -How many inches are there in 2m?

    -How fast in m/s is 10km/hr

    -How many meters in one light year?
    (Speed of light c=3.0x10 to the power of 8m/s)

    I dont need the answer if you choose not to give it but it would help as i would use the answer to see if i am going the right way. But most importantly I need some guidance and help for these questions as I will be tested on these in 3 days. Thnx alot
  2. jcsd
  3. Sep 11, 2007 #2
    Do you know anything about chain conversions?
    since giving away the answer to your problem violates PF guidelines, I will lead with an alternative example.

    How about an easy one to start..
    [tex]1km= ?\ m[/tex]

    Well we already know that [tex]1km=1000m[/tex] that is common knowledge, but how do we get there using a chain conversion?

    You need to set them up as equivalence ratios like this:

    You can read the above statement aloud as "One kilometer (which is what I started with) times 1000 meters 'per' kilometer"

    The reason you can multiply 1km times that fraction is because the fraction (or ratio) [tex]\frac{1000m}{1km}=1[/tex]
    therefor you are not changing the total value...the "km"s just cancel out like parts of fractions.

    Once you can grasp that concept you will be homefree on these.

    Here, try an easier one to start:

    How many seconds are in an hour? try setting up the ratios and we'll help if you need it.

  4. Sep 11, 2007 #3
    Thnx alot That helped a bit
    first for this question i would go 1 hour x 60min/1hour x 60 seconds/ 1min

    and then i would end up with 3600s in 1 hour.

    But when im trying to find inches in 2 meters im lost

    my attempt was 2m x ?\1m

    the "?" i have no clue what goes there, centimeters? and if its centimeters, how much are there in a meter?
    Last edited: Sep 11, 2007
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