8.39. Set Up: (a) Take the direction to be along the final direction of motion of the ball. The initial speed of the ball is zero. (b) Take the direction to be in the direction the ball is traveling before it is hit by the opponent. Solve: (a) (b) Reflect: The signs of and show their direction. This very attainable force has a large effect on the light ball. 140 N is 250 times the weight of the ball. 8.40. Set Up: Take to be upward. Use the motion of the ball after it leaves the racket to find its speed just after it is hit. After it leaves the racket At the maximum height Solve: gives For the interaction with the racket and 8.41. Set Up: The impulse is the area under the versus t curve between and Let the direction be to the left, so is positive. Solve: (a) is positive so the impulse is to the left. (b) (i) so The final velocity of the ball is to the left. (ii) so The final velocity of the ball is to the left. Reflect:
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Trigraph, 4.2 kg, 5 5 m, 5 31 lb, 5 50.0 m, 5 80 m