Draw free body diagrams for the following, that is all.
a) A 784.8 N weightlifter is standing holding a bar weighing 981 N directly over his head (The unknown external force you should include in the FBD is the GRF acting on the weightlifter's feet).
b) An individual is holding her right leg (tibia and fibula) in 20° (clockwise (CW) with respect a right horizontal passing through her knee joint) of knee flexion during the performance of a leg extension exercise with a 133.5 N cuff weight attached to her ankle. The cuff weight is located 39 cm from the knee joint. The weight of the individual's combined leg and foot is 40.7 N and the COM of the combined leg and foot is located 0.236 m from the knee joint. The net muscle force of the quadriceps acting to maintain the current position is 1168 N. The quadriceps muscle force is located 17.4 cm from the knee joint and has a line of action 15° CW with respect to the leg. The unknown external force(s) is/are the net joint reaction forces acting on her knee joint in this position.
c) A rightward force applied to a book in order to move it across a desk at constant velocity.