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Biomechanics
IPHY 4540
Problem Set #7
For all quantitative problems, please list all known variables, the variables that you need to find, and put a box
around your final answers. Answers must include units
. Show the work you did to reach the answer.
1. Since it is nearly World Series time…Jeff Francis pitches a 250gram baseball with a release velocity of 100MPH
(44m/sec). His arm is fully extended at release, and the distance from the ball to his shoulder is 60cm.
A. Assuming his arm to have zero mass, what is the centripetal force that needs to be exerted by his rotator cuff (=
shoulder ligaments and muscles) so that his arm stays attached?
B. More realistically, assume Jeff has a body mass of 70kg. Use table 2.1 of Enoka, p. 67 to calculate the masses of
his upper arm, forearm and hand.
The table gives equations for weights. Convert these weights to kg.
C. His upper arm is 25cm long, his fore arm is 25 cm long and his hand is 10 cm long. Again, use table 2.1 of Enoka
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 '09
 KRAM

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