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# Q6S - − 3 × 10 10 J The orbit is an ellipse with apogee...

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Quiz 6 Solutions Check the best answer. 1. Which of the following is NOT true about Kepler’s laws? All three of the laws are explained by Newton’s law of universal gravitation. The 1 st law says that planetary orbits are ellipses with the sun at the geometric center. [One focus of the ellipse.] The 2 nd law (the law of areas) is a consequence of conservation of angular momentum. One can use the 3 rd law to determine the mass of a planet, to a good approximation, if the planet has a moon of relatively small mass. Check T or F depending on whether the statement is true or false. 2. A person falling feet first in the vicinity of a neutron star (a small but very massive star) would feel weightless, but would experience severe stretching due to tidal forces. T F Physics 53 Summer 2010 1

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3. The total energy of a spaceship’s orbit around the earth is
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Unformatted text preview: − 3 × 10 10 J. The orbit is an ellipse with apogee distance r 2 equal to 3 times the perigee distance r 1 . {All answers are numerical.] a. What is the potential energy at perigee? [Relate r 1 to a and use the general formulas for E and U .] b. What is its kinetic energy at perigee? c. What is the kinetic energy at apogee? a. Since 2 a = 4 r 1 we have GMm 4 r 1 = 3 × 10 10 J. The potential energy at perigee is U ( r 1 ) = − GMm r 1 = 4 E = − 12 × 10 10 J. b. K ( r 1 ) = E − U ( r 1 ) = 9 × 10 10 J. c. Since U ( r 2 ) = − GMm r 2 = − GMm 3 r 1 = 1 3 U ( r 1 ) = − 4 × 10 10 J, we have K ( r 2 ) = E − U ( r 2 ) = 1 × 10 10 J. [Can also use v ( r 1 ) = 3 v ( r 2 ) .] Physics 53 Summer 2010 2...
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