In softball, the pitcher throws with the arm fully extended (straight at the elbow). In a fast pitch the ball leaves the hand with a speed of 139 km/h. (a) Find the rotational kinetic energy of the pitcher’s arm given its moment of inertia is 0.720 kg ? m 2 and the ball leaves the hand at a distance of 0.600 m from the pivot at the shoulder. (b) What force did the muscles exert to cause the arm to rotate if their effective perpendicular lever arm is 4.00 cm and the ball is 0.156 kg?

Step-by-step solution Step 1 of 9 The formula to find the rotational kinetic energy of the arm is, Here, is the moment of inertia of the arm, is the angular velocity of the arm. (a) The formula to find the angular velocity of the arm is, Here is the velocity and is the radius. Step 2 of 9 Substitute for and for Step 3 of 9 Use the formula to find the rotational kinetic energy, Step 4 of 9 Substitute for and for . Therefore, the rotational kinetic energy of the arm is . Step 5 of 9 (b) Here angular acceleration of the arm is calculated using newton’s third law of motion as,