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*12. A golf ball strikes a
hard, smooth floor at an angle of 30.0° and, as the drawing shows, rebounds at the same angle. The mass
of the ball is 0.047 kg, and its speed is 45 m/s just before and after
striking the floor. What is the magnitude of the impulse applied to the golf
ball by the floor? (Hint: Note that only the vertical component of the ball’s momentum
changes during impact with the floor, and ignore the weight of the ball.) |
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Look at momentum before and
after |
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Let’s make up as + and down as -. Since there are no forces
acting in the x direction the momentum in the x direction is not
changed. But
there is a force in the up y direction so the y momentum is changed. Since the x component does not change and
the angle does not change the y component must be the same in magnitude. The impulse-momentum theorem provides |
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From diagram we can see |
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