What is required to calculate the formula for stress on a snatch block performing a vertical lift?

The correct choice involves determining the line pull by multiplying the load weight by the coefficient of friction before applying the standard formula to calculate stress. This is essential because, in a vertical lift scenario, the snatch block experiences forces not just from the weight of the load itself, but also from the frictional interaction between the rope or cable and the snatch block sheave.

The coefficient of friction accounts for the reduction in efficiency due to this friction when lifting the load. By finding the line pull first, you accurately reflect the total force exerted on the snatch block. Once you have the line pull, you can correctly apply the standard stress formula—stress is defined as force divided by area. This ensures that you're considering both the weight of the load and the impact of friction on the lifting process, leading to a more precise calculation for safety and performance in rigging operations.

The other choices do not correctly account for the necessary factors involved in the scenario. For example, multiplying mass by density does not directly relate to calculating the stress under loading conditions. Similarly, using an arbitrary multiplication factor like 25 without context or justification does not provide a reliable method for determining stress in this situation.