Example 10: A 60-lb block is suspended from a cable-pulley system as shown. Determine the force in the pulley strut and the corresponding angle. Ignore the size of the pulley.


We begin by drawing the free-body diagram of the concurrent force system at B.

Free-body diagram:

Since we can ignore the size of the pulley, the angle f can be determined as

Next we write the equations of equilibrium for forces at point B. Note that the tension T in the cable is constant and is equal to the weight of the block.

Rewrite the two equilibrium equations as

and divide them side by side to solve for angle q as

Using the equilibrium of forces in the x direction, we solve for force F as