# Thread: mass and energy query

1. ## 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

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

You are given $\displaystyle E$ and $\displaystyle c$...its just "plug n' chug" from here...

3. What exactly are you having trouble with?

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

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

Just a matter of plugging it in.