Question

In terms of energy, $1u$ is equal to:

• A. $100J$
• B. $931.1kcal$
• C. $931.1MeV$
• D. ${10}^{7}erg$

Answer 1

Answer: (C)

$931.1MeV$

$1u=1.67\times {10}^{-24}g$

Energy equivalent to this mass can be calculated by using the relation:
$E=m{c}^2$

Here, $m=1.67\times {10}^{-24}g$

$c=3\times {10}^{10}cm/s$

$E=1.67\times {10}^{-24}\times {(3\times {10}^{10})}^{2}ergs$

$=\frac{1.503\times {10}^{-3}}{{10}^7}J=1.503\times {10}^{-10}J$

Now, $1.6\times {10}^{-19}J=1eV$

$1J=\frac{1}{1.6\times {10}^{-19}}eV$

$\therefore 1.503\times {10}^{-10}J\Rightarrow 6.25\times {10}^{18}eV$

$=6.25\times {10}^{18}\times 1.503\times {10}^{-10}eV$

$=9.393\times {10}^{8}eV=931.1MeV$