Answer
$E = 9.62\times 10^6$ Hiroshima bomb equivalents
Work Step by Step
$d = E^{1/3},$ where $d$ is in $km$ and $E$ is in megatons of TNT
If $d = 50~km$, then we can find $E$:
$E^{1/3} = d$
$E = d^3$
$E = (50)^3$
$E = 1.25\times 10^5$ megatons of TNT
We can convert this energy to units of Hiroshima bomb equivalents:
$E = (1.25\times 10^8~kilotons~of~TNT)\times (\frac{1~bomb}{13~kilotons ~of~TNT})$
$E = 9.62\times 10^6$ Hiroshima bomb equivalents
