Final answer:
To increase the force along the femur or tibia in a traction setup with the same weight, the number of pulleys should be increased. This applies the principles of mechanical advantage, resulting in a greater output force from the same input weight.
Step-by-step explanation:
The question discusses a traction setup for a broken bone and asks how to increase the force along the femur (or tibia, as mentioned in other parts of the question) using the same weight. According to physics, and specifically the principles of mechanical advantage in pulley systems, the force exerted can be increased by increasing the number of pulleys used in the system. When frictionless pulleys are used in combination, the force applied to the load becomes nearly an integral multiple of the input force, determined by the number of cables that directly pull on the system. Thus, to increase the force with the same weight, one would increase the number of pulleys (option c).