Q: A wire of diameter 1 mm breaks under a tension of 1000 N. Another wire, of same material as that of the first one, but of diameter 2 mm breaks under a tension of
(a) 500 N
(b) 1000 N
(c) 10000 N
(d) 4000 N
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Ans: (d)
Sol: Braking Force ∝ Area of Cross Section
$\frac{F_1}{F_2} = (\frac{r_1}{r_2})^2 $
$\frac{1000}{F_2} = (\frac{1}{2})^2 = \frac{1}{4}$
$ F_2 = 4000 N $