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Midterm2_2004Key0

# Midterm2_2004Key0 - Midterm Exam#2 Biomechanics IPHY 4540...

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Midterm Exam #2 Biomechanics IPHY 4540 Fall 2004 1D. Few Americans get adequate exercise. Mostly, we just sit around. Carefully indicate the whole body center of mass and create a free-body diagram, the system = the whole body. Indicate each external force acting on the system and name each force. 0.25 points x 4 diagrams, = 1.0 points. All force arrows must be drawn at least 1cm long to be graded. extra and/or wrong forces get deducted. i. person sitting on a tall stool in a bar; feet just dangle and do not touch ground com a little forward and higher than anatomical ref position one vertical force pointing down from com = weight= mg one vertical force pointing up at the buttocks = stool reaction force ii. person sitting in a restaurant in a straight backed chair, feet flat on ground com a little more forward and higher than stool one vertical force pointing down from com = weight= mg one vertical force pointing up at the buttocks = chair reaction force one vertical force pointing up at the feet = ground reaction force iii. person sitting in a reclining beach chair com still a little more forward and higher than the chair one vertical force pointing down from com = weight= mg one vertical force pointing up at the buttocks = chair reaction force one vertical force pointing up at the feet = ground reaction force a normal force vector pointing at the back, perpendicular to the back = normal force need some friction forces pointing backwards acting at the feet and buttocks some friction force pointing up and parallel to the chair back iv. same position as iii, but floating in the International Space Station com same as for reclining chair no force vectors should be drawn 1C. One popular form of “exercise” is bowling. When a person bowls, they begin standing with their feet together. Then, they take three walking steps and stop with one foot in front as they release the bowling ball. For this walking, make two plots vs. time (for all three steps): i. the horizontal position of the center of mass & ii. the vertical position of the center of mass Draw the plots one above the other. Don’t worry about the bowling ball or the arm motion, focus on the walking. Indicate the approximate positions in meters, the approximate times and events in the stride (e.g. heelstrike, toe-off) on the axes.

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