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# HW-Ch8 - HW-CH8 9th Edition CH8 Problems 20 40 84 107 8th...

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HW-CH8 9th Edition CH8 Problems: 20, 40, 84, 107 8th Edition CH8 Problems: 26, 38, 70, 77 20. A pendulum consists of a 2.0 kg stone swinging on a 4.0 m string of negligi- ble mass. The stone has a speed of 8.0 m/s when it passes its lowest point. (a) What is the speed when the string is at 60 o to the vertical? (b) What is the greatest angle with the vertical that the string will reach during the stone’s motion? (c) If the potential energy of the pendulum-Earth system is taken to be zero at the stone’s lowest point, what is the total mechanical energy of the system? 40. The potential energy of a diatomic molecule (a two-atom system like H 2 or O 2 ) is given by U = A r 12 ° B r 6 ; where r is the separation of the two atoms of the molecule and A and B are positive constants. This potential energy is associated with the force that binds the two atoms together. (a) Find the equilibrium separation { that is, the distance between the atoms at which the force on each atom is zero. Is the force repulsive (the atoms are pushed apart) or attractive
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