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solutions_for_chapter_8

# solutions_for_chapter_8 - 6 Picture the Problem The...

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6. Picture the Problem : The physical situation is depicted at right. Strategy: Use for the work done by the spring. That way the work will always be negative if you start out at because the spring force will always be in the opposite direction from the stretch or compression. The work done by kinetic friction is , where d is the distance the box is pushed irregardless of direction, because the friction force always acts in a direction opposite the motion. Solution: 1. (a) Sum the work done by the spring for each segment of path 2: 2. Sum the work done by friction for each segment of path 2: 3. (b) Sum the work done by the spring for the direct path from A to B: 4. Sum the work done by friction for the direct path from A to B: Insight: The work done by friction is always negative, and increases in magnitude with the distance traveled. 15. Picture the Problem : The spring is stretched by the applied force and stores potential energy. Strategy: Use equation 6-4 to find the spring constant, and then equation 8-5 to find the stretch distance. Solution: 1. (a) Solve equation 6-4 for k : 2. Solve equation 8-5 for x : 3. (b) Repeat step 2 with the new U : Insight: Notice that in part (b) the stretch distance doubled but the stored potential energy quadrupled because U is proportional to x 2 .

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17. Picture the Problem : The pendulum bob swings from point A to point B and loses altitude and thus gravitational potential energy. See the figure at right. Strategy: Use the geometry of the problem to find the change in altitude of the pendulum bob, and then use equation 8-3 to find its change in gravitational potential energy. Solution: 1. Find the height change of the pendulum bob: 2. Use to find: Insight: Note that is negative because the pendulum swings from A to B. Likewise, is positive and the pendulum gains potential energy if it swings from B to A. 27. Picture the Problem : Three balls are thrown upward with the same initial speed, but at different angles relative to the horizontal. Strategy:
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solutions_for_chapter_8 - 6 Picture the Problem The...

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