CATAGORY: Mechanics
QUESTION: How long would a 100W light bulb burn, on weighing 140g(if the
mass was converted to energy)?

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Ah a good old E = mc^2 problem (here c^2 means c times c).  Since energy
(E) is power (P) times time (t)

(1)           E =Pt

then          

(2)           t = E/P

Since here E = mass (m) times the speed of light (c) squared

(3)            E =mc^2

We can substitute (3) into (2) to give

(4)           t = mc^2/P           

m = 140g =.140kg
c = 3 X 10^8 m/s
P = 100W = 100J/s

Thus 

(5)          t = .140kg X (3 X 10^8 m/s)^2 / 100J/s = 1.26 X 10^14 seconds

But there are 3.1536 X 10^7 seconds in one year so

             t = 1.26 X 10^14 s / 3.1536 X 10^7 s/yr = 3.995 X 10^6 years

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            *  t ~ 4 million years *
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                Impressive Eh?