# Would the energy be in if you used grams for mass and km/sec for c?

• Someone502
In summary, the energy unit would be joules if grams were used for mass and km/sec were used for c. This can be calculated by converting kilometers to meters and using the equation E = mc^2, where E represents energy, m represents mass, and c represents the speed of light. When using kilograms, meters, and seconds, the unit would also be joules. However, if kilometers and grams were used, the unit would be megaJoules due to the squared term in the equation. The amount of energy needed to fuel a light bulb for a certain amount of time depends on the efficiency of the conversion and the power needed to keep the light bulb on.
Someone502
What unit would the energy be in if you used grams for mass and km/sec for c?

And how many lights or something would 1 gram of the energy fuel (for comparision).

Thanks

Last edited:
for kilograms, meters, and seconds, you would get joules. if you use kilometers instead of meters you would be getting kJ, since a kilometer is 1000m. If you use kilometers and grams, you would (I believe) be getting joules, since the "1000" conversion facor for meters -> kilometers and kilograms -> grams cancels.

Your second question can be answered by plugging in the mass in kilograms.

Look at the Joule, the standard unit of energy and see how your units relate.

$$Joule = \frac{m^2*kg}{s^2}$$

Someone502 said:
And how many lights or something would 1 gram of the energy fuel (for comparision).

It depends on how long you want to fuel them for. Lights require a certain amount of energy per second (in mks units, that's "watts") to stay alight. If 1 gram of mass energy were converted with 100% efficiency to power the light, then it could keep a 100-Watt light bulb going for 30,000 years (or 300 for 100 years)!

whozum said:
for kilograms, meters, and seconds, you would get joules. if you use kilometers instead of meters you would be getting kJ,

megaJoules

since a kilometer is 1000m. If you use kilometers and grams, you would (I believe) be getting joules, since the "1000" conversion facor for meters -> kilometers and kilograms -> grams cancels.

not quite. there is a square term in $$E = m c^2$$ for the kilometers that isn't there for kilograms or for Joules.

r b-j

Someone502 said:
What unit would the energy be in if you used grams for mass and km/sec for c?
Why change it? The equation was formulated in the gram/centimetre/second system. Just convert your kilometres to metres first.

Danger said:
Why change it?
The questioner appears to be asking for the purpose of understanding what happens when certain things are done. In this case it pertains to units.
The equation was formulated in the gram/centimetre/second system. Just convert your kilometres to metres first.
The equation was not formulated in terms of any units whatsoever.

Pete

pmb_phy said:
The questioner appears to be asking for the purpose of understanding what happens when certain things are done. In this case it pertains to units.
Sorry; I misunderstood the question.

pmb_phy said:
The equation was not formulated in terms of any units whatsoever.
Perhaps a poor choice of words on my part; when Einstein first used it, those were the units that he employed. You couldn't arbitrarily change it to energy in dynes, mass in metric tonnes, and speed in rods per hour and still get a reasonable result.

## 1. What is the significance of using grams for mass and km/sec for c in terms of energy?

The units of measurement used for mass and velocity can affect the calculation of energy. By using grams for mass and km/sec for c, the resulting energy will be in joules. This is the unit of measurement for energy in the International System of Units (SI).

## 2. How do grams and km/sec relate to the speed of light in energy calculations?

In the famous equation E=mc², c represents the speed of light in a vacuum, which is approximately 299,792,458 meters per second. By using km/sec for c, we are essentially using a conversion factor to convert the speed of light in meters per second to kilometers per second, which is then squared in the equation to calculate energy.

## 3. Can you use other units of measurement for mass and velocity in energy calculations?

Yes, you can use other units of measurement for mass and velocity in energy calculations, but the resulting energy will be in different units. For example, if you use kilograms for mass and meters per second for velocity, the resulting energy will be in joules as well, but the numerical value will be different.

## 4. How does converting units in energy calculations affect the accuracy of the results?

Converting units in energy calculations does not affect the accuracy of the results, as long as the conversion is done correctly. The numerical value of the energy may be different, but the physical quantity remains the same.

## 5. Are there any advantages to using grams for mass and km/sec for c in energy calculations?

One advantage of using grams for mass and km/sec for c in energy calculations is that it is a more convenient and commonly used unit of measurement in scientific research and experimentation. Additionally, using SI units allows for easier comparison and communication of results between scientists.

### Similar threads

• Other Physics Topics
Replies
29
Views
3K
• Other Physics Topics
Replies
18
Views
1K
• Other Physics Topics
Replies
3
Views
971
• Mechanics
Replies
6
Views
1K
• Other Physics Topics
Replies
1
Views
906
• Other Physics Topics
Replies
5
Views
2K
• Linear and Abstract Algebra
Replies
14
Views
1K
• Other Physics Topics
Replies
8
Views
501
• Chemistry
Replies
3
Views
2K
• Other Physics Topics
Replies
4
Views
2K