Question
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One method of pitching a softball is called the "windmill" delivery method, in which the pitcher's arm rotates through approximately 360 degree in a vertical plane before the 198 gram ball is released at the lowest point of the circular motion. An experienced pitcher can throw a ball with a speed of 96.5 mi/h. Assume that the angular acceleration is uniform throughout the pitching motion, and take the distance between the softball and the shoulder joint to be 76.6 cm. Determine the angular speed of the arm in rev/s at the instant of release. Find the value of the angular acceleration in rev/s2 and the radial and tangential acceleration of the ball just before it is released. Determine the force exerted on the ball by the pitcher's hand (both radial and tangential components) just before it is released. Your response differs significantly from the correct answer. Rework your solution from the beginning and check each step carefully. N The correct answer is not zero. N
Explanation / Answer
So the final angular speed is 9.009 rev/sec = 56.605 rad/sec
the avg angular speed was half this 56.605 / 2 = 28.3025 rad/sec
so the time for the acc to occur was 2pi / 28.3025 = 0.222 seconds
So...
(b) alpha = 9.009/0.222 = 40.581 rev/s^2
a c = w^2 r = 56.605^2 * 0.766 = 2435 m/s^2
a t = change in speed / time = ang speed * r / time = 56.605 * 0.76 / 0.222 = 194 m/s^2
(c) F r = mass * a c = 0.198 * 2435 = 482 N
F t = mass * a t = 0.198 * 194 = 38.37 N