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# Dynamical Astronomy

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1. Dynamical Astronomy Multiple Choice Questions

2. Test Question Does this quiz work? A. Yes B. No

3. Dynamical Astronomy • 1. Two solid bodies of a finite mass are held in free space, neither of them start with any movement relative to each other and no other gravitating bodies are there to perturb their motion once released. What will happen when they are released? • They will eventually collide coalesce. • They will move together and go into orbit of each other. • They will eventually collide and stick together. Y • There is not enough information to decide, need to know the ratio of their masses.

4. Dynamical Astronomy • 2. It is only possible to have a perfect circular orbit if the orbiting object is much, much less massive than the object it orbits. • True. • False. y

5. Dynamical Astronomy • 3. “The orbit of each planet is a circle, with the Sun at the focus of each” Is this… • Kepler’s first law. • Kepler’s second law. • Kepler’s third law. • Kepler’s fourth law. • None of the above. y

6. Dynamical Astronomy • 4. Where ‘a’ is the semi-major axis and ‘T’ is the period, Kepler’s third law states that… • a2/T3 = constant • a2 x constant = T3. • a3 x constant = T2. • T2 x constant = a3. y

7. Dynamical Astronomy • 5. Finish off Newton’s second law: “The rate of change of momentum of a body… • …is inversely proportional to applied force, and is in the direction of the force.” • …is proportional to the mass and inversely proportional to the force applied.” • …is proportional to the applied force and is in the direction of the force.” y • None of the above.

8. Dynamical Astronomy • 6. Think about combining the two simple expressions for radial speed in orbital motion and angular velocity, omega. Which of the following expressions is correct? • r = ωv. • ω = rv. • ω = r/v. • r = v/ω. y

9. Dynamical Astronomy • 7. A planet moves around a star at a constant angular velocity. Which of the following statements are true about its motion? • Its force and acceleration are both directed towards the star. y • Its force is directed towards the star but it is not accelerating. • Its acceleration is directed towards the star and its force is directed away from it. • It has a linear acceleration towards the star.

10. Dynamical Astronomy • 8. Where the symbols have their usual meanings, the value for the acceleration due to gravity on a planet’s surface is given by… • GM / R2. y • GM / R. • GMm / R2. • GMm / R.

11. Dynamical Astronomy • 9. By substituting into F = ma it is possible to find an expression for the constant in Kepler’s third law. What is this constant? • GMsun / 4π. • GMsun / πR2. • GMsun / 4π2. y • None of the above.

12. Dynamical Astronomy • 10. Angular momentum is conserved in orbits, true or false? • True. y • False.

13. Dynamical Astronomy • 11. Which of the following statements about orbital eccentricity ‘e’ is FALSE? • If e = 0 we have a circular orbit. • If e << 1 we have a long, thin orbit. • e = 1 corresponds to a parabola. • e < 0 corresponds to a hyperbola. y

14. Dynamical Astronomy • 12. Which of the following statements is true? • The perihelion is the furthest point from the Sun on the orbital path. • The is aphelion is the furthest point from the Sun on the orbital path. y • The perihelion is the furthest point from the centre of the ellipse on the orbital path. • The aphelion is the furthest point from the centre of the ellipse on the orbital path.

15. Dynamical Astronomy • 13. If you are circularly orbiting a planet in a spacecraft, what will happen if you apply a kick in the direction of the motion? • You will move into a larger circular orbit. • You will move into a smaller circular orbit. • You will move into a larger elliptical orbit. y • You will move into a smaller elliptical orbit.

16. Dynamical Astronomy • 14. If you are circularly orbiting a planet in a spacecraft, what will happen if you apply a radial kick outwards? • You will move into a larger circular orbit. • Your semi latus rectum will be preserved. y • Your semi latus rectum will change. • You will move into a smaller elliptical orbit.

17. Dynamical Astronomy • 15. You are on a spacewalk when your lifeline gets cut. You have a tool box. What do you do to get back to the ship? • You throw the tool box away from the space craft. y • You throw the tool box towards the spacecraft. • You leave the tool box behind and perform breaststroke to get you nearer to the ship. • You can’t do anything, you are going to die. • You throw the tool box perpendicularly away from the ship.

18. Dynamical Astronomy • 16. For orbital motion, which of the following statements is true? • Linear momentum will be preserved but angular momentum will not. • Angular momentum will be preserved but linear momentum will not. • Both angular and linear momentum will be preserved. y • Neither angular nor linear momentum will be preserved.

19. Dynamical Astronomy • 17. Which of the following expressions are part of the Virial Theorem for circular orbits? • (mv2)/2 + GMm/r = Constant. • (mv2)/2 – GMm/r = Constant. y • Kinetic energy = + Gravitational potential energy / 2. • None of the above.

20. Dynamical Astronomy • 18. How do you formulate an expression for the escape velocity of a planet? • Multiply the gravitational potential energy by the kinetic energy of the object wanting to be released. • Equate the gravitational potential energy to zero. • Equate the gravitational potential energy to the kinetic energy of the object wanting to be released. y • Add the gravitational potential energy to the kinetic energy of the object wanting to be released.

21. Dynamical Astronomy • 19. The orbit of the Moon about the Earth can be assumed to be circular because of their very large difference in mass, true or false? • True. • False. y

22. Dynamical Astronomy • 20. Which of the following superheroes would be able to escape the Earths gravitation with a single jump (no propulsion allowed)? • Superman – starting jump speed 8000 m/s. • Iron man – starting jump speed 1000 m/s. • A Glasgow university student being thrown by the Hulk – starting throw speed 500 m/s. • Dr Martin Hendry – starting jump speed 14000 m/s. (Don’t tell anyone, it’s a secret.) y • All of the above. • None of the above. • Can’t tell, you would need to know their mass.

23. Dynamical Astronomy • 21. What is the expression for the velocity in a general elliptical orbit? • v2 = GM x (2/r – 1/a). y • v = GM x (2/r – 1/a). • v2 = GM x (1/a – 2/r). • v = GM x (1/a – 2/r).

24. Dynamical Astronomy • 22. How do you complete a Hohmann transfer orbit? • First boost the speed in the low earth orbit, once at perigee boost speed again to stay in a larger circular outer orbit. • First boost the speed in the low earth orbit, once at apogee boost speed again to stay in a larger circular outer orbit. y • First boost the speed in the low earth orbit, once at apogee reduce speed to stay in a larger circular outer orbit. • First boost the speed in the low earth orbit, once at perigee reduce speed to stay in a larger circular outer orbit.

25. Dynamical Astronomy • 23. Which statement is FALSE about gravity assist of planet for spacecraft? • The spacecraft when it flies by a planet must have a greater speed than the escape speed of that planet. • Gravity assist means that interplanetary missions can be greatly sped up. Y • Gravity assist can be used to change the direction of the spacecraft and the speed. • If the planet is moving in the opposite direction to the spacecraft at the time of the fly by, the speed of the spacecraft will not be increased.

26. Dynamical Astronomy • 24. Planetary assist greatly reduces the amount of fuel that is required for interplanetary missions, true or false? • True. y • False.

27. Dynamical Astronomy • 25. In an elliptical orbit how are the angular momentum ‘L’ of the orbiting object and the semi latus rectum ‘r0’ related? • L is directly proportional to r0. • L is inversely proportional to r0. • L2 is directly proportional to r0. y • L2 is inversely proportional to r0. • None of the above.