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4. A single-start, square-threaded power screw has the following baseline character- istics: Outside diameter pitch, p Load, W 25.4 mm 5.08 mm 1500 N thread friction coefficient 0.08 collar friction coefficient collar diameter 0.04 28 mm (a) What torque, TR, total, is required to raise the load? Include units. (b) What torque, TL, total, is required to lower the load? Include units (c) Suppose the screw runs at 100 rpm for ten seconds, raising the load. How much energy is required to drive the screw. Include units. (d) Referring to the previous problem, how much work was done on the load? ) What is the efficiency of the screw? (f) Show by a calculation whether or not this screw is self-locking. Describe what it means for a power screw to be self-locking 5. A square-threaded power screw has a mean diameter, dm 1.75 in and a pitch p 0.875 in. The coefficient of thread friction is 0.10 and the collar friction is negligible. What horsepower is required to raise a weight of 3000 lbf at a rate of 20 ft/min?

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