Help filling in a formula correctly? Not sure about SI units etc

In summary: That gives you the density in meters^-3.In summary, The task at hand is to calculate the Jeans mass of a diffuse hydrogen cloud with a particle density of 3e7 cm^-3 and a temperature of 150 K. The Jeans mass is calculated using the formula (5kT/GmewM(H))^(3/2) . (3/4∏p)^(1/2), where k is the Boltzmann constant, T is the temperature in Kelvin, G is the gravitational constant, mew is the mean molecular weight, m(H) is the mass of gas particles, and p is the cloud mass density. The mean molecular weight and mass of gas particles can be found by looking up the properties
  • #1
daleklama
33
0

Homework Statement



It is estimated that a particular diffuse hydrogen cloud has a particle density of 3e7 cm^-3, and the temperature is 150 K.
Calculate Jeans mass.

Homework Equations



Jeans mass is given by: (5kT/GmewM(H))^(3/2) . (3/4∏p)^(1/2)

where k = boltzmanns constant = 1.38e-23
T = temperature in Kelvin = 150K
G = Gravitational constant = 6.673e-11
mew = mean molecular weight = ?
m(H)= mass of gas particles = ?
p = cloud mass density = ?


The Attempt at a Solution



I know I just have to fill in the formula, so it should be simple, but I'm really having trouble calculating the parts of the formula.

I don't have a clue about mean molecular weight OR mass of gas particles, and I THINK the 'cloud mass density' is the number given in the question (3e7 cm^-3) but I don't understand how to convert that to metres (the unit cm^-3 is throwing me off.

I really want to calculate this as accurately as I can, could anyone help please?

Thank you.
 
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  • #2
daleklama said:
I don't have a clue about mean molecular weight OR mass of gas particles,
You know that the gas is hydrogen, so look it up, keeping in mind that hydrogen gas is H2.

and I THINK the 'cloud mass density' is the number given in the question (3e7 cm^-3) but I don't understand how to convert that to metres (the unit cm^-3 is throwing me off.
Express the centimeter in meters, then cube it.
 

FAQ: Help filling in a formula correctly? Not sure about SI units etc

What are SI units and why are they important in filling in a formula correctly?

SI units, or the International System of Units, are a standardized system of measurement used by scientists and researchers around the world. They provide a consistent and universal way to express physical quantities in a formula, ensuring accurate and precise results.

How do I determine which SI units to use in a formula?

The SI unit for a given physical quantity is determined by its base unit, such as meters for length or kilograms for mass. When filling in a formula, make sure the units for each variable match the base unit for that physical quantity.

What do the different prefixes in SI units mean?

SI units use prefixes to represent values that are either very large or very small. For example, "kilo" represents 1000 and "milli" represents 0.001. These prefixes are used to convert between different units within the same physical quantity.

How do I convert between SI units?

To convert between SI units, you can use the prefixes or conversion factors. For example, to convert from meters to kilometers, you can divide by 1000 or use the prefix "kilo." It is important to keep track of units and cancel them out appropriately in order to get the desired result in the correct unit.

What are some common mistakes to avoid when filling in a formula with SI units?

Some common mistakes to avoid include forgetting to convert between units, mixing up prefixes, or using the wrong base unit. It is also important to pay attention to the order of operations when solving a formula, as well as properly representing significant figures in the final result.

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