Question

In a nuclear reaction, 2.50 x 1012 joules of energy have been released. What does this value equate to in kilograms?
(1 J = 1 kg m2/s2)


8.33 x 104 kg

7.5 x 1020 kg

2.25 x 10-4 kg

2.78 x 10-5 kg

Answer 1

Einstein's formula: \[E = mc ^{2}\]
\[(2.50 x 10^{12} J) = (m)(3.00 x 10^{8} m/s)^2\]
\[m = 2.78 x 10^{-5} kg\]

In the future, could you show the exponent scientific notation like this:

2.50 x 10^12? (not 2.50 x 1012)

It is a lot easier to read. Thanks.

Answer 2

Yeah, sorry. Thank you.

Answer 3

Where did the 3.00 come from?
And the 10^8?

Answer 4

Good question, that probably seemed liked it came out of nowhere. \[c\] is a constant that represents the speed of light. It is about 3.00 x 10^8 m/s. In the formula, it needs to be squared.

Answer 5

Oh, okay thank you, again.

Answer 6

Also what are the steps on how you got 'm' by itself?

Answer 7

to start:

(2.50x10^12 J) = (m)(3.00x10^8 m/s)^2

then square c:

(2.50x10^12 J) = (m)(9.00x10^16 m/s)

next divide both sides by c^2:

(2.50x10^12 J)/(9.00x10^16 m/s) = (m)

and the division yields the answer:

m = 2.78x10^−5 kg

(you know the units are in kg when they make that mention of 1 J = 1 kg m^2/s^2 at the end of the question.

Answer 8

Okay, thank you, again.