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lecture16

# lecture16 - Energy Conservation 1 Mechanical energy...

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Unformatted text preview: Energy Conservation 1. Mechanical energy conservation U K E For closed isolated system U K E 2. Open system ext W E U K int 3. Conservative and nonconservative forces • Forces such as gravity or the elastic force, for which the work dose not depend on the path taken but only on the initial and final position, are called conservative forces •For conservative forces the work done on a closed path (a lop) is equal to zero •Friction is a nonconservative force noncons W E int cons W U Example: A block is moved from rest at point A to rest at point B. Which path requires the most work to be done on the object? A) The table is leveled and friction is present. Path 1 Path 2 Path 3 All the same B) The table is tilted and frictionless . Path 1 Path 2 Path 3 All the same 1 2 3 A B k friction W m g x x x = 0, equilibrium k m μ k v? Example: A 5.00 g block is pushed against a spring with k = 8.00 N/m. The spring is initially compressed 5.00 cm and then released. The coefficient of kinetic friction between the block and the table is 0.600. What is the speed of the block at x = 0? 2 2 k 1 1 2 2 mv kx mgx 2 initial 1 2 E kx 2 final 1 2 E m v 2 2 (8.00 N/m)(0.05 m) 2(0.600)(9.81 m/s )(0.05 m) 1.85 m/s 0.005 kg v 2 k 2 kx v g x m Example:...
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lecture16 - Energy Conservation 1 Mechanical energy...

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