07_InstSolManual_PDF_Part21 - Work and Energy 7-21 1 35 N...

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7.93. Set Up: First set the final kinetic energy of the object to one half of the initial elastic potential energy: or Solving for the speed, Solve: Reflect: This gives and The object has moved 3.5 cm, less than half the total distance of 12.0 cm. 7.94. Set Up: Applying in part (a), since both spring forces are to the left. In part (b), use For part (c), apply the conservation of energy to obtain where the mass of the ball is Solve: (a) (to the left) (b) (c) 7.95. Set Up: Apply the adapted version of the conservation of energy for nonconservative forces: where and Solve: (a) Solve for the initial velocity to determine the driver’s speed at impact: The driver was thus 15 mph over the posted speed limit at the instant he struck the pedestrian. (b) The driver must pay a ticket fine of 7.96. Set Up: Use the principles of energy conservation with 1, 2, 3, and 4 representing the energy states as shown in the schematic and Figure 7.96 Solve: Since the ball loses 25% of its maximum potential energy. Similarly, and, neglecting air drag, thus the ball also loses 25% of its kinetic energy. The loss of speed is determined by examining kinetic energy:
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