oldfinal 01 CC09-solutions

oldfinal 01 CC09-solutions - Bodet(ngb299 – oldfinal 01...

This preview shows pages 1–3. Sign up to view the full content.

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: Bodet (ngb299) – oldfinal 01 CC09 – turner – (57340) 1 This print-out should have 22 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 10.0 points Determine W (or fuel energy) required to launch a satellite of mass m at rest from a launching pad placed at the surface earth, to a circular orbit where the radius of the orbit is r = 3 R where R is the radius of the earth. Ignore the effect of the Earth’s rotation. The fuel energy required is 1. 5 GmM 6 R correct 2. 2 GmM R 3. 7 GmM 6 R 4. GmM R 5. GmM 6 R 6. 3 GmM 4 R 7. 3 GmM 2 R 8. GmM 4 R Explanation: The orbital satellite energies are E f =- GM m 2 r =- GM m 6 R E i =- GM m R . The fuel energy is W = E f- E i =- GM m 6 R-- GM m R = 1- 1 6 GmM R = 5 GmM 6 R . 002 10.0 points A pendulum consists of a very light sti ff rod with negligible mass of length L = 1 . 9 m hanging from a nearly frictionless axle, with a mass m = 0 . 5 kg at the end of the rod. Suppose you hit the stationary hanging mass so that it has an initial speed v i . What is the minimum initial speed in order that the pendulum go over the top ( θ = 180 ◦ )? (in units of m/s) L m s = Lθ O θ Correct answer: 8 . 63 m / s. Explanation: Let : m = 0 . 5 kg , L = 1 . 9 m , and g = 9 . 8 m / s 2 . Energy principle leads K f + U f = K i + U i . For present problem, K f = 0, U f- U i = mg (2 L ), this leads to K i = U f- U i = mg (2 L ) mv 2 i 2 = mg (2 L ) v i = 4 g L = 4 (9 . 8 m / s 2 ) (1 . 9 m) = 8 . 63 m / s . 003 10.0 points Consider a electron-electron interaction sys- tem. Which figure given below represents the Bodet (ngb299) – oldfinal 01 CC09 – turner – (57340) 2 system. In each figure K, U and K+U are rep- resented by the y-axis and the separation by x-axis. Choices: 1. A 2. C 3. D correct 4. B Explanation: Notice figure D contains all expected fea- tures of electron-electron interaction. Begin with some finite K at large r. As the two electrons approach each other, r decreases and K decreases. Eventually they stop at the distance of the closest approach, where K=0. K+U= constant. At K=0, the value of K+U line is determined by the U value there. U has the characteristic behavior of a sys- tem with a repulsive force, with U > throughout. As the separation gets closer and closer, the magnitude of U increases cor- respondingly. We reject the choices of figures A, B and, since each figure contains at least an error. Notice that in figure A, U < 0. But for electron-electron case, we must have U > 0. In figure B, K < 0. But K = mv 2 2 , which can never be negative. In figure C, as r approaches infinity K > K + U . This is again false. As r approaches infinity we should have instead, K+U ap- proaches K, since here U approaches 0....
View Full Document

{[ snackBarMessage ]}

Page1 / 13

oldfinal 01 CC09-solutions - Bodet(ngb299 – oldfinal 01...

This preview shows document pages 1 - 3. Sign up to view the full document.

View Full Document
Ask a homework question - tutors are online