Q. If the speed of light were 2/3 of its present value, the energy released in a given atomic explosion will be decreased by a fraction of

(a) 2/3

(b) 4/9

(c) 4/3

(d) 5/9

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Ans: (b)

Sol: E = mc

^{2}$ \displaystyle E’ = m (\frac{2 c}{3})^2 $

$\displaystyle E’ = \frac{4}{9}m c^2 $

$ \displaystyle E’ = \frac{4}{9} E $