747. What is the stress on the hauling part when lifting a 4,200 lbs. weight using a threefold purchase rove to advantage? (Allow 10 percent of the weight per sheave for friction.)

The stress on the hauling part is calculated by accounting for friction in a threefold purchase rove to advantage. With 7 supporting parts and 10% of the 4,200 lb load allowed for friction in each of the 6 sheaves, the effective load becomes 6,720 lb, resulting in a hauling part tension of 960 lb.