Find the greatest length of copper wire, that can hang without breaking. Breaking stress `=7.2 xx 10^(7) N//m^(2)`. Density of copper `7.2 g//c c. g=10 m//s^(2)`.

Explanation

Given,
Breaking stress, `S=7.2 xx 10^(7) N//m^(2)`,
Density of wire, `rho = 7.2 g//c c = 7.2 xx 10^(3) kg//m^(3)`
Let l be the greatest length of wire that can hang without breaking and A be the area of cross section of the wire.
Weight of wire = `(A l) rho g`.
Breaking stress,
`S=("weigth of wire")/("area of cross section")=(A l rho g)/(A)`
or `l=(S)/(rho g) = (7.2 xx 10^(7))/((7.2 xx 10^(3)) xx 10) =1000m`.