Homework 3

- A weight lifter is lifting a total of 175kg in a bench press. The bar is 25kg, however he put the weights on wrong and has 90kg on the right side and 60kg on the left side. His hands are positioned as shown. What is the force in each of his arms? Where would he need to place his hands to make the force in each arm equal? Is that possible given this setup?

- Two forces act on the femur as shown below. Determine the resultant moment they create at the femoral head (assume the head is fixed). Express the moment in vector format. F1 is {-60i+35j+15k}lb and F2 is {45i+40j-23k}lb.

- A runner impacts the ground as shown here. Determine the force and moment at the hip. Assume the foot (CD) weighs 8kg and is 0.34m in length. The calf segment (CB) is 12kg and is 0.5m in length. The upper leg (AB) segment weighs 20kg and is 0.63m in length. The force acts 0.02m from the tip of the foot. What are two possible ways the runner could reduce the forces and moments at the hip.

- A soccer player kicks a ball at the same time he is hit from a slide tackle. Determine the forces and moments at the hip. Assume the foot (segment CD) weighs 7 kg and is 0.29m in length. The calf segment (CB) is 10.5kg and 0.45m in length. The upper leg (segment AB) is 22kg and is 0.71 m in length. The forces act as indicated. The force of the kick act at the end point of the toe, and the force of the slide tackle acts 0.38m from point C.

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