# Converting probs

#### nutsy76

I am having problems on conversion factors. I don't even know where to begin with my problems. I know which formulas to use I just don't know what to do after that. For ex I am working on this prob:

A Grand Prix racer completes a 500 km race in 2hr 15min. What is the average speed of the car in km per hr and meters per sec?

Like I said I know what formula to use but what are the steps to convert? I keep getting stuck on how to start.

Thanks.

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#### OlderDan

Homework Helper
nutsy76 said:
I am having problems on conversion factors. I don't even know where to begin with my problems. I know which formulas to use I just don't know what to do after that. For ex I am working on this prob:

A Grand Prix racer completes a 500 km race in 2hr 15min. What is the average speed of the car in km per hr and meters per sec?

Like I said I know what formula to use but what are the steps to convert? I keep getting stuck on how to start.

Thanks.
All conversions should be thought of as a series of multiplications by factors equal to one. Here is an example I recently did

$$a = \frac{{45\frac{{mi}}{h}}}{{1s}} = \frac{{45mi}}{{hs}}\left( {\frac{{5280ft}}{{mi}}} \right)\left( {\frac{{12in}}{{ft}}} \right)\left( {\frac{{2.54cm}}{{in}}} \right)\left( {\frac{{1m}}{{100cm}}} \right)\left( {\frac{1 h}{{60\min }}} \right)\left( {\frac{{1\min }}{{60{\mathop{\rm s}\nolimits} }}} \right) = 20.1\frac{m}{{s^2 }}$$

Every term in parentheses is equal to one because the numerator is equal to the denominator. It is simply a matter of choosing to write the fractions in such a way that units you want to replace divide out and the units you want to convert to are left. See if you can follow this model and do your problem.

You will have to express your time either in hours or in minutes by doing a prliminary conversion of one of those and adding them together.

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