# mass and energy query

• December 14th 2008, 11:12 AM
trigger
mass and energy query
According to Einstein’s equation, what mass is equivalent to an energy of
6.7 × 10–14 J? You should use a value for c of 3.0 × 108 m s–1
and can you please give your answer in kilograms, in scientific notation and to two significant figures.

thx trigger
• December 14th 2008, 11:19 AM
Chris L T521
Quote:

Originally Posted by trigger
According to Einstein’s equation, what mass is equivalent to an energy of
6.7 × 10–14 J? You should use a value for c of 3.0 × 108 m s–1
and can you please give your answer in kilograms, in scientific notation and to two significant figures.

thx trigger

Since $E=mc^2$, and you want mass....we see that $m=\frac{E}{c^2}$

You are given $E$ and $c$...its just "plug n' chug" from here...
• December 14th 2008, 11:21 AM
o_O
What exactly are you having trouble with?

$E = mc^2 \ \Leftrightarrow \ m = \frac{E}{c^2}$

You have the energy (note that a joule can also be expressed in SI units: $kg \cdot m^2 \cdot s^{-2}$ ) and you have the speed of light.

Just a matter of plugging it in.