HW #6-1-solutions - pasha (sep635) HW 6-1 Antoniewicz...

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1 This print-out should have 21 questions. Multiple-choice questions may continue on the next column or page – fnd all choices beFore answering. 001 (part 1 of 3) 2.0 points An electron has mass 9 . 1 × 10 - 31 kg. The speed oF light is 3 × 10 8 m / s. IF the electron’s speed is 0 . 982 c (that is, v/c =0 . 982), what is its particle energy? Correct answer: 4 . 33607 × 10 - 13 J. Explanation: The electron’s particle energy, or total en- ergy, is given by E = γ mc 2 = 1 s 1 - ± v c ² 2 mc 2 = 1 p 1 - 0 . 982 2 (9 . 1 × 10 - 31 kg) c 2 = 4 . 33607 × 10 - 13 J . 002 (part 2 of 3) 2.0 points What is its rest energy? Correct answer: 8 . 19 × 10 - 14 J. Explanation: The rest energy is given by E r = mc 2 =(9 . 1 × 10 - 31 kg)(3 × 10 8 m / s) 2 = 8 . 19 × 10 - 14 J . 003 (part 3 of 3) 1.0 points What is its kinetic energy? Correct answer: 3 . 51707 × 10 - 13 J. Explanation: The kinetic energy is just the di f erence be- tween the particle energy and the rest energy: K = E - E r =4 . 33607 × 10 - 13 J - 8 . 19 × 10 - 14 J = 3 . 51707 × 10 - 13 J . 004 (part 1 of 4) 2.0 points The point oF this question is to compare rest energy E r and kinetic energy KE at low speeds. A baseball is moving at a speed oF 11 m / s. Its mass is 150 g (0 . 15 kg). The speed oF light is 3 × 10 8 m / s. What is its rest energy? Correct answer: 1 . 35 × 10 16 J. Explanation: The rest energy is given by E rest = mc 2 =(150g)(3 × 10 8 m / s) 2 = 1 . 35 × 10 16 J . 005 (part 2 of 4) 1.0 points Is it okay to calculate its kinetic energy using the Formula 1 2 mv 2 ? 1. Yes, because | ~ v | ± c . correct 2. Yes, because accuracy isn’t too important here. 3. No, because | ~ v | ± c . 4. No, because baseballs are not subatomic particles Explanation: It’s okay to use the approximate Formula here, because the baseball’s speed is so small compared to the speed oF light. 006 (part 3 of 4) 1.0 points What is its kinetic energy? Correct answer: 9 . 075 J. Explanation:
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This note was uploaded on 11/17/2011 for the course PHY 303K taught by Professor Turner during the Fall '08 term at University of Texas at Austin.

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HW #6-1-solutions - pasha (sep635) HW 6-1 Antoniewicz...

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