A 35mm diameter steel cable carries a mine skip to a depth of 625m. The mass of the skip is equal to the mass of the 625m length cable. The unit mass of the steel cable is 7.85 x 10^3 kg/m^3 . The cable unwinds from the surface. Calculate the extension in:

a) The full length of the cable

b) When the cable is extended for half itslength, (present your answers in mm).

Assume E for the steel cable = 210000N/mm^2 and use g = 10m/s^2

When I try to do this :

7.85 * 10^3 = 7850

1kg = 9.81N

7850 * 9.81 = 77008.5 N

Stress = Force/Area

Area = π * (35)^2/4 = 962.1127502

77008.5/962.1127502 = 80.04103468

E = Stress/Strain

Strain = Stress/E

80.04103468/210000 = 3.811477842^-04 or 0.0003811477842

625 * 1000 = 625000

Strain = Change in Length/Length = 0.0003811477842 * 625000 = 238.2173651

The answer is 292mm but, I keep getting 238mm. I do not knowwhere I am going wrong. Also, I have no idea how to answer part B. The answer to this is 109mm. Please can anyone help?

Instead of using 1kg = 9.81 N. I used 10 as it does state use g = 10m/s^2 But, I still got 242 instead of 292.