4. If the load has a weight and the system is in the equilibrium position shown, what are the probabilities of failure if the allowable tensions of AB is 25 lb and AC is 22 lb in the cables, respectively?

Solution

There are three forces acting on A, as shown in the figure below.

So we have

From above equations, , . With , we have

For cable AB, the probability of failure is

Ans.

For cable AC, the probability of failure is

Ans.