1. Problem 5. 5 page 154 - The femur is in static equilibrium
Problem 5.5 page The femur is in static equilibrium. We can use Equation 5.1 on page 126
The direction of the force the femur exerts on the patella is indicated roughly on the previous diagram. The sum of the x-components of the forces must be zero. This gives
Solving for
The sum of the y-components of the forces must be zero also. This gives
The magnitude of the force by the femur on the patella is then
Assess:  This result is reasonable in magnitude, considering the magnitude of the forces exerted by the tendons and their directions.