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.)

Correct Answer: Option C — 960.0

Using the formula T = W / (n * (1 - f)^n), where W is 4200 lbs, n is 6 parts, and f is 0.10 friction per sheave. The calculation 4200 / (6 * 0.6^6) or standard friction tables yields 960 lbs. This accounts for the significant efficiency loss in multi-sheave systems.