1. SMDEP Physics Gravity: Orbits, energy

2. Ch 6, #27 (b) only: mass of stars? 1.9x10 28 kg 2.9x10 26 kg 3.5x10 26 kg 4.5x10 24 kg 5.Other 6.Didn’t finish

3. Ch 6, #51: surface gravity of white dwarf? 1.4.4x10 7 m/s 2 2.4.4x10 4 m/s 2 3.4.4x10 10 m/s 2 4.4.4x10 2 kg m/s 2 5.Other 6.Didn’t finish

4. Ch 6, #62: mass of black hole? 1.9x10 28 kg 2.1x10 27 kg 3.5x10 26 kg 4.5x10 39 kg 5.Other 6.Didn’t finish

5. Ch 9, #69 (a) only: center of mass? 1.4.7x10 7 m 2.4.7x10 4 m 3.4.7x10 6 m 4.4.7x10 10 m 5.Other 6.Didn’t finish

6. Applications of Gravity: Astronomy Orbital speeds determine masses –Galaxies –Galaxy clusters –Supermassive black holes –Extrasolar planets Motion of star about center of mass

8. Suppose the Earth had no atmosphere and a ball were fired from the top of Mount Everest tangent to the ground. If the initial speed was large enough to cause the ball to move in a circular trajectory around the Earth, the ball’s acceleration would: 1.Be much less than g (because the ball doesn’t fall to the ground) 2.Be approximately g 3.Depend on the ball’s initial speed

9. The Moon does not fall to Earth because: 1.The net force on it is zero 2.It is beyond the main pull of Earth’s gravity 3.It is being pulled by the Sun and other planets as well as Earth 4.All of the above 5.None of the above

10. Two satellites A and B with equal mass are orbiting the Earth in circular orbits. The distance of satellite B from the center of the Earth is twice that of satellite A. What is the ratio of the centripetal force acting on B to that acting on A? 10 0 of 70 1.1/8 2.1/4 3.1/2 4.(1/2) 1/2 5.1 A B r B =2r A

11. Two satellites A and B with equal mass are orbiting the Earth in circular orbits. The distance of satellite B from the center of the Earth is twice that of satellite A. What is the ratio of the tangential speed acting on B to that acting on A? 10 0 of 70 1.1/8 2.1/4 3.1/2 4.(1/2) 1/2 5.1 A B r B =2r A

12. A rock, initially at rest with respect to the Earth and located an infinite distance away, is released from rest and falls in a straight line to Earth. Compared to the rock’s speed when it hits the surface of the Earth, its speed when it passes a point 3 Earth radii above the earth’s surface is: 10 0 of 70 RERE 4R E 2R E 3R E 1.½ as much 2.1/3 as much 3.1/4 as much 4.1/9 as much 5.1/16 as much

13. For a projectile to escape from the Earth, it must have an initial velocity larger than the escape velocity. On which of the following does the escape velocity (at the surface of the Earth) depend? 10 0 of 70 1.The radius of the Earth 2.The mass of the Earth 3.The mass of the projectile 4.Both 1 and 2 5.1, 2, and 3