Suppose the force acting on a tennis ball (mass 0.040 kg) points in the +x direction and is given by the graph of Fig. 7-30 as a function of time. a) Use a graphical method to estimate the total impulse given the ball._____N·s (b) Use a graphical method to estimate the velocity of the ball after being struck, assuming the ball is being served so it is nearly at rest initially._________m/s