Exam 1 practice problems solutions

Exam 1 practice problems solutions - Exam 1 practice...

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Exam 1 practice problems solutions Physics 204 1. Nuclear fusion is a highly sought after alternate energy source because it is environmentally friendly and uses very abundant fuels. However, it is a technical challenge to get two atomic nuclei to fuse. One way to get two nuclei to fuse is to strip off their electrons then accelerate the nuclei to high speed and collide them together. Using this idea it is possible to fuse two deuterium nuclei into helium. Deuterium is an isotope of hydrogen, having one proton and one neutron in its nucleus. a. If the two deuterium nuclei need to get within 15 1.3 10 m of each other for them to fuse into helium, predict what speed they must be fired at to get that close. b. Describe any assumptions you made in making your prediction. Use energy principles with the system being the two deuterium nuclei. The initial state of the system will be the two nuclei very far apart. The final state of the system will be after the helium nucleus has formed.           ,, 2 2 , 2 2 , 2 9 2 19 2 , 27 27 15 6 , 0 1 2 0 0 2 8.99 10 1.602 10 1.673 10 1.675 10 1.3 10 7.28 10 if i E i f E f D D D i f p n D i f w Di p n f E W E K U K U q m v k r e m m v k r N m C C ke v m m r kg kg m v m s     In making this prediction I had to assume the two deuterium nuclei were far enough away that the electric potential energy between them was approximately zero. I also assumed the two nuclei were point-like. Lastly, I assumed the two nuclei were fired at each other exactly head on. 2. A carbon dioxide (CO 2 ) molecule consists of two oxygen atoms and one carbon atom in the arrangement shown. Oxygen atoms are more electronegative than carbon atoms, which effectively makes the ends of the molecule slightly negatively charged ( 20 2.00 10 C  ) and the center of the molecule slightly positively charged ( 20 4.00 10 C  ). a. Using the details of this model of the CO 2 molecule, make a conceptual argument for what direction the electric field points at location A. b. Predict the mathematical value of the electric field at the point indicated. The electric field at point A is a superposition of the contributions to the electric field from the three charged particles. The positively charged carbon atom’s contribution will point in the positive y direction. The left negatively charged oxygen atom’s contribution will point in down and to the left. The right oxygen’s atom’s will point down and to the right. O O C 10 1.16 10 m A 11 5.00 10 m
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The horizontal components of the contributions from the oxygen atoms will cancel, leaving a net downward component.
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Exam 1 practice problems solutions - Exam 1 practice...

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