Pedro Martinez pitches a 250 gram baseball with a release velocity of 100MPH (44

Question

Pedro Martinez pitches a 250 gram 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 60 cm.
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? solve for Newtons & convert to pounds.

B. More realistically, assume Pedro has a body mass of 70 kg. 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 25 cm long, his forearm is 25 cm long and his hand is 10 cm long. Again, use table 2.1 of Enoka and calculate the location of the center of mass of each of the segments, upper arm, fore arm and hand.

D. Combine all this information and re-calculate the centripetal force at his shoulder. You need to calculate 4 forces and add them. His hand is traveling at 100MPH, but you need to calculate the velocities of the center of mass of his upper arm, and of his forearm.

Explanation / Answer

wewe can find here only the centripetal force as the table mentioned is not accessible to us. As for as centripetal force is concerned, it is given by F = mv2/r

Where distance between ball and shoulder will serve as radius r. Hence m = 250 gem = 0.25kg, v = 44m/s,

and r = 60 cm = 0.6m so F = 0.250 x 442/0.6 = 806.67Newton

F = 806.67 x 0.224 = 180.7 pound force

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