Question

 In softball, the pitcher throws underhand with the arm fully extended (straight at the elbow). In a fastpitch the ball, of mass m=0.156 kg, leaves the hand at a speed of 139 km / h, when the arm is pointed vertically downward.

Part (a) Find the rotational kinetic energy, in joules, of the pitcher's arm-ball system, given that the arm's moment of inertia is 0.72 kg · m² and the ball leaves the hand at a distance of 0.725 m from the pivot.

Part (b) What force, in newtons, do the muscles exert to cause the arm to rotate, assuming the force is constant and its effective perpendicular lever arm is 3.8 cm? Assume also that the pitcher's arm starts extended horizontally behind her at rest and the ball is released at the bottom of the swing, as described in part (a). Approximate the arm as a uniform rod.

Answer 1