Asbestos is a fibrous silicate mineral with remarkably high tensile strength. But it is no longer used because airborne asbestos particles can cause lung cancer. Grunerite, a type of asbestos, has a tensile strength of 15 x 102 kg/mm2 (thus, a strand of grunerite with a 1-mm2 cross-sectional area can hold up to 15 x 102 kg). The tensile strengths of aluminum and Steel No. 5137 are 25 x 104 Iblin2 and 5.0 x 104 Iblin2, respectively. Calculate the cross-sectional area (in mm2) of wires of aluminum and of Steel No. 5137 that have the same tensile strength as a fiber of grunerite with a cross-sectional area of
1.0 micro. mZ

Area of aluminum = 8.53 * 10⁻⁶ mm²

Area of steel = 4.27 * 10⁻⁶ mm²

Explanation:

1 in² = 645.16 mm²

1 lb = 0.453592 kg

Tensile strength of Grunerite = 1.5 * 10² kg/mm²

Tensile strength of aluminum = 2.5 * 10⁴ lb/in²

Tensile strength of aluminum = 2.5 * 10⁴ * (0.453592 kg/lb /645.16 mm²/in²)

Tensile strength of aluminum = 17.58 kg/mm²

Tensile strength of Steel No. 5137 = 5.0 * 10⁴ lb/in²

Tensile strength of Steel No. 5137 = 5.0 * 10⁴ * (0.453592 kg/lb /645.16 mm²/in²

Tensile strength of Steel No. 5137 = 35.15 kg/mm²

Area of Grunerite = 1.0 μm² = 10⁻⁶ mm²

Mass of Grunerite = area * tensile strength

mass of Grunerite = 10⁻⁶ mm² * 1.5 * 10² kg/mm² = 1.5 * 10⁻⁴ kg

Area of aluminum of same tensile strength as Grunerite = mass of Grunerite/ tensile strength of aluminum

Area of aluminum = 1.5 * 10⁻⁴ kg /  17.58 kg/mm²

Area of aluminum = 8.53 * 10⁻⁶ mm²

Area of Steel No. 5137 of same tensile strength as Grunerite = mass of Grunerite/ tensile strength of aluminum

Area of steel = 1.5 * 10⁻⁴ kg /  35.15 kg/mm² = 8.53 * 10⁻² mm²

Area of steel = 4.27 * 10⁻⁶ mm²

i believe you are right for all except the 3rd ( look at sqdancefan his answer is much better)

pre-sliced bread is a relatively recent development in baking technology. previous to that, it was always sold in a bakery in daily-made contiguous loaves with no wrapping, and was moderately perishable, usually being used with a day or two (which is why every bakery had a discounted “day-old” bread table.) therefore, pre-sliced bread would grow stale quickly. the hard crust provided a protective layer, and once the exposed dry slice left from the previous cut was removed, the interior was still soft.

what keeps bread soft is the moisture retained in the crumb (the light spongy part that’s not crust). the reason the crust develops is the surface of the dough gets exposed to hot dry air during baking which browns the outer layer and seals it, preventing all the moisture from escaping the dough. longer exposure to air will also eventually cause your bread to lose flavor and become stale.

people were used to cutting slices as they needed them and storing bread in a specially-made wooden or metal breadbox or pail with a lid to preserve it longer, but the first automatically sliced commercial loaves were produced on july 6, 1928, in chillicothe, missouri, using a machine invented by otto rohwedder, an iowa-born, missouri-based jeweler.[1] pre-sliced bread would indeed dry out, were it not for another 20th century technology: the plastic bag. bread could now be pre-sliced, and if the enclosing bag remains sealed as much as possible, the bread will remain soft and fresh for longer than if sitting unwrapped on a shelf or enclosed in a bread box that is not air-tight. sealed packaging meant bread could also be sold on store shelves and eliminate frequent trips to a bakery.

sealing bread in a plastic bag had another effect: the moisture in the loaf will re-distribute into the crust and soften it, which is sometimes more pleasing in a sandwich - especially for children whose teeth might not yet be strong enough to tear through a hard crust. a homemade loaf of bread can be sealed in a bag overnight and the crust will become soft like store-bought sandwich bread.

these were novel changes in how bread was produced and sold, which led to the coining of the phrase “the greatest thing since sliced bread.”