# hw4 - point approximately 9 cm from the center of the...

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ME 577 – Human Motion Kinetics Homework #4 Due Wednesday, March 2, Midnight 1. Assume that a child is hit by a truck moving at 5 m.p.h. The child’s total height is 4 ft. 8 inches, their weight is 55 lbs., and the impact point coincides with her center of mass. What is the speed of the child’s head when she hits the ground if we model the child as a single link? First, assume a pivot at the feet. 2. What if the same child is struck, but his or her feet are lifted off the ground so that there is no pivot point? 3. Model an adult as a two segment system (pivot at the hips). Assume that he or she is run under by a car traveling at 30 mph. What is the speed of the person’s head when it hits the hood of the car. Use a joint reaction model at the hips. 4. A weight lifter starts with his hands at his sides and raises his arms 90 o in T=1 second, . His arm is 80 cm long and rotates about the center of the humeral head. The deltoid attaches at a

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Unformatted text preview: point approximately 9 cm from the center of the humeral head. For simplicity, assume that it always makes an angle of 10 o with the long axis of the humerus. The weight lifter raises a weight with a mass of 30 kg. 4a. Draw a free body diagram (single force no moment assumption). 4b. Write out the equations of motion that govern the system. 4c. Calculate the acceleration of the center of mass. 4d. If the mass of the arm is 8 kg, determine the systems moment of inertia relative to the center of the humeral head. 4e. Determine the contact forces in the shoulder and the muscle forces in the deltoid. ! ( t ) = " 4 1 # cos t T \$ % & ' ( ) \$ % & ' ( ) 5. In class we considered what happens to the force in the PCL when someone is kneeling or drops to their knees. Draw a better free body diagram than the one we developed in class. If we could only add one additional muscle or ligament to the problem, which one would it be?...
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hw4 - point approximately 9 cm from the center of the...

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