Simple Machines - Biomechanics of the Human Body - page 90

In this case, both pulleys are fixed and, hence, just change the direction of
the forces. Thus, it is possible to exert forces of traction of the same value
as the suspended weights, each one with 60 N. The resultant force of traction
will be horizontal, directed to the left whose magnitude is given by the law
of cosines.

q

60N

2 2

cos 30 ∘

T ¼ ð Þ þ ð 60N Þ þ 260N ð Þ ð 60N Þ ¼ 115 9N

: :

Example 5.2 An equivalent arrangement of Example 5.1 is shown in the figure of
Example 5.2. Here the pulleys are placed in different positions and a single cable is
utilized with one extremity attached to the wall and the other sustaining the weight
for the traction.

15°
15°

6 kg

In this configuration a single weight is used to exert two forces of the same
magnitude of 60 N each, whose resultant is 115.9 N, that is, greater than the load
itself.

Example 5.3 Analyze now a system of pulleys, shown in the figure of Example 5.3,
used for traction of an immobilized femur.