[Physics] How to convert from an arbitrary set of units to the desired set

homework-and-exercisesunit conversion

I'm having trouble solving this Physics question with "made up" units. Here is the problem and my work so far.

The Omicronians have told you that they use the units: $$\\{OP=7.29\frac{flurg}{grom^2}}$$ These units need to be converted to meters/second^2 and their respective values are:

5.24 flurg = 1 meter

1 grom = 0.493 second.

Question: What is the value of OP in meters/second^2?

Below is one of my many failed attempts at solving this. Do I actually square the value of "grom" or leave it in the same format as m/s^2? Either way, my answer was still incorrect when I tried to square the denominator, leading me to believe I've gone wrong elsewhere.

$$\\{7.29\frac{5.24m}{0.493s^2}} = 77.48m/s^2$$

Best Answer

$$\require{cancel}$$

The trick to unit conversions is to think of it as multiplying by 1. When you have $$5.2\ flurg = 1\ meter,$$ that also means that $$\frac{5.24\ flurg}{1\ meter} = 1$$ and $$\frac{1\ meter}{5.24\ flurg} = 1.$$ This is important because converting units does not change the quantity, only the paper-and-pencil representation. Which ratio you use depends on how you want the units to cancel (which works just like canceling numbers in fractions). So, for every unit you want to convert, set up a ratio like one of the above and multiply it by the original quantity to get a new quantity in new units.

For example, $1\ foot = 12\ inch$. So, to convert 1.5 feet to inches $$1.5\ feet \underbrace{\left(\frac{12\ inch}{1\ foot}\right)}_{=\ 1} = 1.5\ \cancel{feet} \left(\frac{12\ inch}{1 \cancel{foot}}\right) = 18\ inch$$ Notice that using the other ratio leads to a useless answer: $$1.5\ feet \underbrace{\left(\frac{1\ foot}{12\ inch}\right)}_{\textrm{also 1, but not helpful}} = 0.125\ \frac{feet^2}{inch}$$

For units with powers, use the same power on the conversion ratio. $$9.8\ \frac{m}{s^2}\left(\frac{60\ s}{1\ min}\right)^2 = 3.5\cdot10^4\ \frac{m}{min^2}$$

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