Which of these correctly describes whether a girl holding a ball in the same position is doing work on the ball? a. the girl is doing work on the ball because the energy of the ball changed, even though it is not displaced. b.the girl is doing work on the ball because the energy in her muscles changed, even though the ball is not displaced. c.the girl is doing no work on the ball because she is not exerting any net force on the ball. d.the girl is doing no work on the ball because the ball is not displaced.

Review multiple-concept example 7 in this chapter as an aid in solving this problem. in a fast-pitch softball game the pitcher is impressive to watch, as she delivers a pitch by rapidly whirling her arm around so that the ball in her hand moves in a circle. in one instance, the radius of the circle is 0.626 m. at one point on this circle, the ball has an angular acceleration of 66.1 rad/s2 and an angular speed of 12.6 rad/s. (a) find the magnitude of the total acceleration (centripetal plus tangential) of the ball. (b) determine the angle of the total acceleration relative to the radial direction.