Newbie Questions about Units in Physics Equations

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In the equation E=mc^2, E represents energy in joules, m is mass in kilograms, and c is the speed of light in meters per second. The equation maintains consistency across different unit systems, such as SI and cgs, where energy, mass, and speed are defined in their respective standard units. To solve for mass when energy is known, one can rearrange the equation; for example, if E is 500 joules, the mass can be calculated using the speed of light as approximately 3,000,000 m/s. The discussion highlights the importance of understanding unit systems and their conversions in physics equations. Accurate calculations depend on correctly applying these units to derive meaningful results.
Incognito310
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In an equation like E=mc^2, what are the units?

Like, I know c is a constant, but in the equation is it meters-per-second, kilometers per hour, or what? In this, and other equations how do you know what is meant by the letters in terms of their computational value?

If E is 500 joules, what is m?
 
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You know that is work A[J]=F[N]*s[m]
=> J=kg* (m/s)^2
From here you can see that if the c is in m/s them mass must be in kg.
 
Incognito310 said:
In an equation like E=mc^2, what are the units?
In any "coherent" system of units, (i.e. in a system where the unit of energy is one unit of mass times one unit of distance squared divided by one unit of time squared) the E will be the standard unit of energy, the m will be the standard unit of mass and the c will be the speed of light measured in the standard units of distance per standard units of time.

In SI, E would be in Joules, m would be in kilograms and c would be in meters per second.
In cgs, E would be in ergs, m would be in grams and c would be in centimeters per second.

You could choose to express E in foot pounds, m in slugs and c in feet per second and the equation would hold.

If E is 500 joules, what is m?

c is 3,000,000 meters per second. Solve for m in kg. The answer will be fairly small.
 
jbriggs444 said:
c is 3,000,000 meters per second. Solve for m in kg. The answer will be fairly small.

It is? Light's gotten pretty slow since lunchtime.
 
Forgot two 0's there jbriggs...
 
Matterwave said:
Forgot two 0's there jbriggs...

So I did. *blush*
 

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