A wide receiver 180cm tall and 75kg was running forward at 15mph, and turned his

Question

A wide receiver 180cm tall and 75kg was running forward at 15mph, and turned his body 180 degrees to catch a ball. After catching it he lost balance and fell backwards onto the ground. Assume that his body did not move horizontally during the fall, and pivot point of body rotation during the fall is his left foot and took 0.2 seconds. Assume that the whole body acts as a rigid body during the fall, and center of gravity of whole body is about an inch above the belly button.

Using reasonable anatomical and engineering assumptions, determind the G force on the back of his head at the moment of impact. Hint: First determine the angular velocity of center of gravity of whole body at ground impact. Use link to determine weight of body parts http://www.exrx.net/Kinesiology/Segments.html

Explanation / Answer

angular velocity of center of gravity of whole body at ground impact = (9.8/0.8534) * 0.2

                                                                                                              = 2.296 rad/sec

=> velocity of head at it hits ground = 1.80 * 2.296

                                                             =   4.1328 m/sec

=> G force on the back of his head at the moment of impact = 0.0826 * 75 * 4.1328/0.2

                                                                                                 = 128.013 N

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