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Homework Help: Simple conversion

  1. Oct 31, 2006 #1
    If i could get anyone to double check my answers on the following it would be a big help. thanks

    On planet Z, the standard unit of length is the foose. Ann the
    Astronaut is 5.90 feet tall on
    earth. She lands on planet Z and is measure to be 88 foosi
    (plural of foose) tall. Her crew
    member Rachael is 94 foosi tall. How tall is Rachael in Earth

    i get 6.3 feet

    5.9/88 = 14.92

    94/14.92 = 6.3

    is this correct? thanks in advance
    Last edited: Oct 31, 2006
  2. jcsd
  3. Oct 31, 2006 #2
    Note the expression: y = A/x2. Which statement is most consistent
    with this expression?

    a. y is less than x
    b. if x is halved, y is multiplied by 4
    c. y is greater than x
    d. if x is doubled, y is multiplied by a factor of 2
    e. y is equal to x

    I find that A seems to be true,, but the wording on D confuses me a bit.
  4. Oct 31, 2006 #3
    OOOOPS, give me a moment... I'm rusty with LaTeX

    It's always a good idea to write your units down when you're doing calculations. The technique I teach is "multiply by 1"... that is, if the numerator = the denominator, the value of the fraction is one.
    [tex]\frac{3 feet}{36 inches}=1[/tex] because the numerator equals the denominator.

    Now, all you have to do is worry about the units you don't want cancelling out each step of the way.

    You could use [tex]\frac{88 foosi}{6.90feet}[/tex] as a multiplier, or you could use [tex]\frac{6.90feet}{88 foosi}[/tex] as a multiplier (to multiply by 1.

    Now, you're starting with [tex]\frac{94 foosi}{1}[/tex] If you multiply it like this: [tex]\frac{94 foosi}{1}*\frac{88 foosi}{6.90 feet}[/tex], then your units work out to foosi squared per foot. Not what you want.

    So, you multiply [tex]\frac{94 foosi}{1}*\frac{6.90 feet}{88 foosi}[/tex] And, your units work out to feet.

    for what it's worth, "5.9/88" is not "= 14.92". You meant 88/5.9
    Last edited: Oct 31, 2006
  5. Oct 31, 2006 #4
    [tex]\frac{5.90 feet}{88 foosi} = \frac{x feet}{94 foosi}[/tex]

    [tex]88 foosi\,x = (5.9 feet)(94 foosi)[/tex]

    [tex]x = \frac{(5.9 feet)(94 foosi)}{88 foosi}[/tex]
    Last edited: Oct 31, 2006
  6. Oct 31, 2006 #5
    :) Or you could do it as a proportion as Geoff did... The proportion method is easier for this type of a conversion; my method above works very well if you're converting something like miles per hour to meters per second.
  7. Oct 31, 2006 #6
    where did you get 6.9? is that a typo? did you mean 5.9?

    anyway, I run the numbers geoff did and I get 6.3 again..so I assum my answer is correct. thanks for the help
  8. Oct 31, 2006 #7
    Yes, your answer's correct.
  9. Oct 31, 2006 #8
    yes, 6.9 was a typo... or rather, a memory problem. :)
  10. Oct 31, 2006 #9
    great thanks.. one other quick question: can I just multiply 3.47 m/s/s by 5 seconds to get my speed after that amount of time? for example:

    . A European sports car dealer claims that his car will accelerate
    at a constant rate from rest
    to a speed of 100 km/hr (28 m/s) in 8.00 s. What is the speed
    after the first 5.00 s of

    a.44.4 m/s b. 34.7 m/s c. 28.7 m/s d. 17.4 m/s e. 8.7

    First I find the acceleration to be 3.47 m/s^2 now can i just times by 5? If so i get 17.4 m/s Is this correct?
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