Compute the torque required to lower the load with the screw from Problem 5.

Data in Problem 5.

If an Acme-thread power screw is loaded in tension with a force of 30 000 lb, what size screw from Table 17–1 should be used to maintain a tensile stress below 10 000 psi? 

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TABLE 17-1 Preferred Acme Screw Threads Nominal major diameter, D (in) 1/4 5/16 3/8 7/16 1/2 5/8 3/4 7/8 1 1/ 13/ 2 23 3 4 Threads per in, n 16 14 12 12 10 8 6 6 5 5 5 4 4 4 4 3 3 3 2 2 2 2 2 5 aPer inch of length of engagement. Pitch, p = 1/n (in) 0.0625 0.0714 0.0833 0.0833 0.1000 0.1250 0.1667 0.1667 0.2000 0.2000 0.2000 0.2500 0.2500 0.2500 0.2500 0.3333 0.3333 0.3333 0.5000 0.5000 0.5000 0.5000 0.5000 Minimum minor diameter, D, (in) 0.1618 0.2140 0.2632 0.3253 0.3594 0.4570 0.5371 0.6615 0.7509 0.8753 0.9998 1.0719 1.1965 1.4456 1.6948 1.8572 2.1065 2.3558 2.4326 2.9314 3.4302 3.9291 4.4281 Minimum pitch diameter, D, (in) 0.2043 0.2614 0.3161 0.3783 0.4306 0.5408 0.6424 0.7663 0.8726 0.9967 1.1210 1.2188 1.3429 1.5916 1.8402 2.0450 2.2939 2.5427 2.7044 3.2026 3.7008 4.1991 4.6973 Tensile stress area, A, (in²) 0.026 32 0.044 38 0.065 89 0.097 20 0.1225 0.1955 0.2732 0.4003 0.5175 0.6881 0.8831 1.030 1.266 1.811 2.454 2.982 3.802 4.711 5.181 7.388 9.985 12.972 16.351 Shear stress area, Aç (in²)a 0.3355 0.4344 0.5276 0.6396 0.7278 0.9180 1.084 1.313 1.493 1.722 1.952 2.110 2.341 2.803 3.262 3.610 4.075 4.538 4.757 5.700 6.640 7.577 8.511