At what angle does the anchor take 100% of the load?

At what angle does the anchor take 100% of the load?

• A. At 120 degrees
• B. At 90 degrees
• C. At 60 degrees
• D. At 150 degrees

Answer: (A)

When two rope legs pull on an anchor with equal tension, the force on the anchor is the vector sum of those two pulls. If each leg has tension T and the angle between them is θ, the anchor experiences F = 2T cos(θ/2). Plugging in 120 degrees for the angle, cos(60°) = 0.5, so F = 2T × 0.5 = T. That means the anchor’s load equals the load carried by a single leg, i.e., 100% of that leg’s load. At smaller angles the anchor load grows above a single leg’s load; at larger angles it drops below. So 120 degrees is the angle where the anchor carries the same load as one leg, hence 100% of that load.

When two rope legs pull on an anchor with equal tension, the force on the anchor is the vector sum of those two pulls. If each leg has tension T and the angle between them is θ, the anchor experiences F = 2T cos(θ/2).

Plugging in 120 degrees for the angle, cos(60°) = 0.5, so F = 2T × 0.5 = T. That means the anchor’s load equals the load carried by a single leg, i.e., 100% of that leg’s load.

At smaller angles the anchor load grows above a single leg’s load; at larger angles it drops below. So 120 degrees is the angle where the anchor carries the same load as one leg, hence 100% of that load.