GENERAL MOTION/FORCES ----------------------- Orbital Motion: -------------- Kepler's 3d law (that the period squared is proportional to the semi-major axis cubed) does NOT apply to the motion of: a) a satellite around the Earth b) a comet around the Sun c) one star about another in a binary star system d) one galaxy about another $e) all of the above apply A description for the relationship between the period of revolution P and the distance from the center R of a point on a record on a turntable would be a) P^2 is proportional to R^3 b) P^2 is proportional to R c) P is proportional to R $d) P does not depend on R A spacecraft in one stable orbit moves to another stable orbit that has twice the semi-major axis as the first. The period of the second orbit is ____ times that of the first orbit. a) 0.5 b) 2 c) cube root of 64 $d) square root of 8 Since angular momentum is conserved, the rotational speed of a collapsing gas cloud a) depends on its mass $b) increases c) decreases d) is independent of its initial rotation Since angular momentum is conserved, the orbital speed of a planet at perihelion as compared to aphelion $a) is larger b) is smaller c) is the same d) approaches infinity A planet at perihelion has a value of X for its angular momentum. when the planet is at aphelion, its angular momentum will be a) less than X. b) greater than X. $c) equal to X. d) cannot tell without further information. If the Sun were suddenly replaced by a solar-mass black hole, the Earth would a) move off the current orbit in a straight line $b) remain in the same orbit c) move into a smaller orbit d) be pulled into the black hole An artifical satellite passes near Jupiter and gains some orbital energy in a `slingshot effect'. What is the effect on Jupiter? a) cooling b) none $c) the effects are minimal because of the small satellite mass d) faster rotation e) Jupiter will revolve about the Sun faster A bowling ball and a paper bag are pushed out of the airlock of a tourist spaceship. The spaceship is coasting with its engines off, halfway along on a weeklong cruise to the Moon. After ten minutes, $a) both objects are still moving together alongside the spaceship. b) the bowling ball is still moving alongside the spaceship, but the paper bag has been left far behind. c) both objects are far behind the spaceship. d) the bowling ball is falling back towards Earth, while the paper bag is still coasting alongside the spaceship. For some reason, you wake up alone in space, twirling a ball on a string, far from any planet, satellite, or massive object. The string breaks. Assuming you would care under such circumstances, what path does the ball take? a) It moves directly away from you in a straight line from the point where the string broke. $b) It moves away from you sideways in a straight line from the point where the string broke. c) It continues to move in the circle because space is frictionless. d) It moves in a paraboloid arc, like a baseball on Earth. Forces and acceleration: ------------------------- Which situation(s) does NOT describe an acceleration: $a) a car traveling with constant speed on a straight road b) a car traveling with constant speed around a bend c) a planet traveling in its orbit around the Sun d) a car decreasing speed on a straight road e) an electron traveling around a nucleus. A piece of toast held at rest above the kitchen floor has $a) potential energy only b) kinetic energy only c) both potential and kinetic energy d) neither, only thermal energy Two identical spacecraft are to be accelerated by rockets. The first rocket fires with a force four times as great as the second. The acceleration of the first rocket is _______ as large as the acceleration of the second. a) 1/4 $b) 4 times c) 1/2 d) 2 times e) None of the above Two Toyotas collide and come to a dead stop. How much more kinetic energy is lost in this collision than in one between two identical cars each moving at half the velocity? a) two times larger b) two times smaller $c) four times larger d) four times smaller e) unchanged, since the potential energy, not the kinetic energy, depends on velocity Electromagnetism is $a) sometimes a repulsive force and sometimes an attractive force. b) always a repulsive force. c) always an attractive force. d) none of the above. The electromagnetic force does not dominate the everyday world because a) it is too weak. b) it acts only over short distances. $c) positive charges cancel the effects of negative charges. d) it only affects magnetic materials. Of the four fundamental forces of nature, the one that is inherently the weakest (with the smallest coupling constant) is the a) strong nuclear force. b) weak nuclear force. c) electromagnetic force. $d) gravitational force. Which of the four fundamental forces of nature has the largest effect on objects at astronomical distances from each other? a) The strong nuclear force. b) The weak nuclear force. c) The electromagnetic force. $d) The gravitational force. The force that holds molecules together is the a) strong nuclear force. $b) electromagnetic force. c) centrifugal force. d) gravitational force. For the strong nuclear force to hold together two protons, they must be a) moving slowly b) moving rapidly $c) close together d) of opposite charge If the distance between two protons is increased by a factor of 10, the (gravitational/electromagnetic) force between them is decreased by a factor of a) 10/ 100 b) 100/ 10000 c) 10000/ 10000 $d) 100/ 100 You are an astronaut taking a spacewalk to fix your spacecraft with a hammer. Your lifeline breaks and the jets on your back pack are out of fuel. To return safely to your spacecraft (without the help of someone else), you should a) throw the hammer at the space ship to get someone's attention. $b) throw the hammer away from the space ship. c) use a swimming motion with your arms. d) kiss your ship good bye. If the strong nuclear force were weaker than the electromagnetic force at the scale of an atomic nucleus then fusion reactions would $a) not be possible b) happen all the time c) not change, since this is already true d) be caused by the electromagnetic force instead Gravity: --------- Gravity is a) sometimes a repulsive force and sometimes an attractive force. b) always a repulsive force. $c) always an attractive force. d) none of the above. The force of gravity is responsible for a) holding the planets near the Sun. b) the tides c) holding the Moon near the Earth d) Two of the above $e) A, B, and C A person is standing on the roof of a one-story building. The ground floor of the building has to support a) no weight. b) less weight than the roof. c) the same amount of weight as the roof. $d) more weight than the roof. The reason that visitors to the south pole do not fall off the planet is that a) atmospheric pressure is larger at the south pole. b) gravity points down and so do the visitors. $c) gravity does not come from off the planet, it comes from the center of the Earth. d) centrifugal force caused by the planet's rotation keeps them there. When you are on the top floor of a building, your weight is _______ when you are on the ground floor. a) much greater than b) very slightly greater than c) equal to $d) very slightly less than e) much less than The Apollo astronauts repeated the experiment that Galileo performed at the Leaning Tower of Pisa by dropping a feather and a hammer on the Moon. The feather and hammer reached the ground at the same time because: a) gravity on the Moon is less than on Earth b) the force of gravity is larger on the feather than on the hammer $c) the acceleration of each object is the same d) the astronauts showed Galileo's experiment to be false. The escape velocity from the Moon is less than that from the Earth because of the Moon's a) lower density $b) smaller mass c) smaller radius d) higher temperature e) distance from the Earth If the size of the Earth were to double (with the mass unchanged), the gravitational attraction of the Sun a) would double b) would decrease by two times c) would increase by four times d) would decrease by four times $e) not change If the radius of the Earth were to double, with no change in its mass, a person's weight would a) be unchanged. b) increase by factor of 4 $c) decrease by a factor of 4 d) double e) be cut in half Antimatter is identical to matter except that its electrical charge is opposite. Suppose that the Moon suddenly changed to antimatter. How might the Moon's orbit change? a) Instead of being attracted to the Earth, the Moon would be repelled and move away. b) Since matter and antimatter attract, the Moon would move closer to the Earth. $c) Since the Moon is neutral, the orbit would not change. d) The Moon and perhaps the Earth would annihilate in a gigantic explosion. Use your knowledge of the escape velocity equation to answer the following. Planet X is twice as massive as the Earth and four times as large as the Earth. Which of the following is true? The escape velocity of X is a) greater than Earth's escape velocity. b) the same as Earth. $c) less than Earth's escape velocity. If woman A approaches man B at a distance C, the gravitational force between them a) exceeds their weight $b) quadruples as C halves c) is proportional to the sum A+B d) is proportional to the distance C squared Suppose that you are in a spaceship traveling past two different planets. You pass within 1 AU of a blue planet which has twice the mass of the Earth, and within 1 AU of a red planet which has the same mass as the Earth. From which planet will you feel the greater gravitational pull? $a) the blue planet b) the red planet c) the gravitational pull from each planet will be equal. If one could magically turn off gravity the Earth would a) leave the solar system along a line connecting the Earth and Sun b) spiral out of control and leave the solar system in a chaotic path $c) travel in a nearly straight line along its present velocity perpendicular to a line connecting Earth and Sun d) move outwards to collide with the Moon Compared to your mass here on Earth, your mass out in the space between the stars would be __________. a) zero b) negligibly small c) much much greater $d) the same e) the question cannot be answered from the information given The Moon's tidal forces cause the Earth's rotation to slow and the Moon to $a) decrease its orbital speed and increase its distance b) decrease its orbital speed and decrease its distance c) slow its rotation d) do nothing (no effect) At different times during its trip, a space probe passes two moons (X and Y) that are identical in size. Though the probe passes both at the same distance, ground control finds that the probe's trajectory is deflected more by moon X than moon Y. Planet X must $a) be denser than planet Y. b) be rotating more quickly than planet Y. c) be less massive than planet Y. d) has less of a magnetic field than planet Y.