Me again

How do I convert the following units

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- Jun 8th 2008, 06:32 AMmoolimanjConverting Units
Me again

How do I convert the following units - Jun 8th 2008, 01:29 PMReckoner
To convert units, treat the units as variables, and use a "conversion factor" to cancel out the old units. For example:

$\displaystyle 18\text{ in} = 18\text{ in}\left(\frac11\right) = 18\text{ in}\left(\frac{1\text{ ft}}{12\text{ in}}\right)$

$\displaystyle = \frac{18\text{ in}\cdot\text{ft}}{12\text{ in}} = \frac{18}{12}\cdot\frac{\text{in}\cdot\text{ft}}{\ text{in}} = \frac32\cdot\frac{\not\text{in}\cdot\text{ft}}{\no t\text{in}} = \frac32\text{ ft}$

Similarly, for number 2:

$\displaystyle 1\frac{\text{BTU}\cdot\text{in}}{^\circ\text{F}\cd ot\text{ft}^2\cdot\text{hr}}$

$\displaystyle = 1\frac{\text{BTU}\cdot\text{in}}{^\circ\text{F}\cd ot\text{ft}^2\cdot\text{hr}}

\left(\frac{1054.8\text{ J}}{1\text{ BTU}}\right)

\left(\frac{1\text{ W}\cdot\text{s}}{1\text{ J}}\right)

\left(\frac{1\text{ ft}}{12\text{ in}}\right)^2

\left(\frac{1\text{ in}}{0.0254\text{ m}}\right)

\left(\frac{9^\circ\text{F}}{5\text{ K}}\right)

\left(\frac{1\text{ hr}}{3600\text{ s}}\right)

$

And, as long as I didn't make a mistake in typing all of that, all of your units should cancel and you will be left with units of $\displaystyle \text{W}\text{m}^{-1}\text{K}^{-1}$. The other questions are fairly similar. - Jun 10th 2008, 06:42 AMmoolimanj
Thanks but I dont understand where the 18 came from. Can you please explain. Also, for part b, why has 32 pounds per square inch been converted accrding to BTU?

Can you please explain with detailed working/wording?

Many thanks - Jun 10th 2008, 08:03 AMReckoner
It was an example that I made up on the spot (convert 18 inches to feet) just to illustrate the basic process.

That work is actually for part (i) (when I said it was for the second part that was a typo; I apologize). The working for the second part is quite similar.