plz try to solve ths problem on elasticity????

Question

what would b da greatest length of a steel wire which at one end can hang freely without breaking? density of steel =7800kg/m^3.breaking stress of steel=7.8X 10^8 N/m cube. . ...answer is 10.20 km..plz try hard

Answer 1

Weight = mass density * area * length * g

Stress = weight / area = density * length * g

length = stress / (density * g)

They give you the stress (with incorrenct units--it should be force per area, not force per length) and the density. You know g. Plugnchug.

Answer 2

weight of wire = area x L x 7800kg x gravity
stress in wire = weight / area
7.8x10^8 = (area x L x 7800 x g)/area
area cancels
7.8x10^8=L x 7800 x 9.81
L = 7.8x10^8 / (7800 x 9.81) = 1.02x10^4meters