Halliday/Resnick/Walker Fundamentals of Physics 8 th edition

Halliday/Resnick/WalkerFundamentals of Physics 8th edition • Classroom Response System Questions Chapter 13 Gravitation Interactive Lecture Questions

13.2.1. A cannon fires a ball vertically upward from the Earth’s surface. Which one of the following statements concerning the net force acting on the ball at the top of its trajectory is correct? a) The net force on the ball is instantaneously equal to zero newtons at the top of the flight path. b) The direction of the net force on the ball changes from upward to downward. c) The net force on the ball is less than the weight, but greater than zero newtons. d) The net force on the ball is greater than the weight of the ball. e) The net force on the ball is equal to the weight of the ball.

13.2.2. If an object at the surface of the Earth has a weight W, what would be the weight of the object if it was transported to the surface of a planet that is one-sixth the mass of Earth and has a radius one third that of Earth? a) 3W b) 4W/3 c) W d) 3W/2 e) W/3

13.2.3. Two objects that may be considered point masses are initially separated by a distance d. The separation distance is then decreased to d/3. How does the gravitational force between these two objects change as a result of the decrease? a) The force will not change since it is only dependent on the masses of the objects. b) The force will be nine times larger than the initial value. c) The force will be three times larger than the initial value. d) The force will be one third of the initial value. e) The force will be one ninth of the initial value.

13.2.4. Two satellites of masses m and 2m are at opposite sides of the same circular orbit about the Earth. Which one of the following statements is true? a) The magnitude of the gravitational force is greater for the satellite of mass 2m than it is for the other satellite. b) The magnitude of the gravitational force is the same for both satellites; and it is greater than zero newtons. c) Since the satellites are moving at a constant velocity, the gravitational force on the satellites must be zero newtons. d) The magnitude of the gravitational force is greater for the satellite of mass m than it is for the other satellite. e) The satellite of mass 2m must move faster in the orbit than the other and eventually they will be on the same side of the Earth.

13.2.5. An astronaut, whose mass on the surface of the Earth is m, orbits the Earth in the space shuttle at an altitude of 450 km. What is her mass while orbiting in the space shuttle? a) 0.125m b) 0.25m c) 0.50m d) 0.75m e) m

13.3.1. When considering the gravitational force acting on a group of particles or an extended body, how does Newton’s law of gravitation apply? a) An extended body is broken down into infinitesimal particles that are mathematical points and massless. Under these conditions, Newton’s law of gravitation is applied to each particle; and the net force is the sum of the individual forces. b) If an extended body can be broken down into spherical particles then, Newton’s law of gravitation is applied to each particle; and the net force is the scalar sum of the individual forces. c) An extended body is broken down into infinitesimal particles. Under these conditions, Newton’s law of gravitation is applied to each particle; and the net force is the vector sum of the individual forces.

13.4.1. Your weight here in the classroom is W. What would your weight be if you were orbiting the Earth in the Space Shuttle at an altitude of 400 km? a) 0.46W b) 0.89W c) W d) 0.97W e) zero

13.5.1. How does the Earth’s gravitational force on you change, if at all, as you drill deeper into the Earth’s crust and descend? a) It remains constant. b) It decreases with increasing depth. c) It increases with increasing depth.

13.6.1. Consider the following pairs of objects with varying masses and separation distances. Which of these pairs has the smallest gravitational potential energy? a) 1 b) 2 c) 3 d) 4 e) 3 and 4 are equally small

13.6.2. In the distant future, a space ship will leave the Earth and travel to a planet where the acceleration due to gravity is one-third that on Earth, By what factor is the required velocity altered to leave the distant planet than it was to leave Earth? a) 1/3 b) 31/2 c) 1 d) 31/2 e) 3

13.6.3. In a distant solar system where several planets are orbiting a single star of mass M, a large asteroid collides with a planet of mass m orbiting the star at a distance r. As a result of the collision, the planet is knocked out of its orbit, such that it leaves the solar system. Which of the following expressions gives the minimum amount of energy that the planet must receive in the collision to be removed from the solar system? a) b) c) d) e)

13.7.1. A spacecraft is in low orbit of the Earth with a period of approximately 90 minutes. By which of the following methods could the spacecraft stay in the same orbit and reduce the period of the orbit? a) Before launch, increase the mass of the spacecraft to increase the centripetal force on it. b) Remove any unnecessary equipment, cargo, and supplies to reduce the mass and decrease its angular momentum. c) Fire rockets to increase the tangential velocity of the ship. d) None of the above methods will achieve the desired effect.

13.7.2. A star is believed to be orbiting a black hole in an orbit as shown. If the star is at the point in its orbit and is slowing down as it moves clockwise, where is the black hole most likely to be located?

13.7.3. A planet is following a slightly elliptical orbit as it orbits the Sun. Which of the following explanations best explains why the planet moves faster in its orbit when it is closest to the Sun? a) Because no external forces are acting on the system, the total linear momentum of the system must be conserved. b) The gravitational attraction between the planet and the Sun results in a torque on the planet and the total angular momentum of the system is not conserved. c) Because no external forces are acting on the system, the total angular momentum of the system must be conserved. d) Because the system is isolated, the total kinetic energy of the planet must be conserved. e) Because the mass of the planet is not uniformly distributed, the gravitational force on the planet will vary the most when it is far from the Sun and least when it is close to the Sun.

13.7.4. Which one of the following statements concerning a planet orbiting the Sun is true? a) The gravitational force between the planet and Sun must be larger than the centripetal force needed to keep the planet in its orbit. b) The centripetal force that keeps the planet moving in a stable orbit is provided by the gravitational attraction between the planet and Sun. c) If the gravitational force between the planet and Sun is less than the centripetal force needed to keep the planet in its orbit the planet would spiral in until the planet reaches a stable orbit. d) The gravitational force of the planet that acts on the Sun is always smaller than the gravitational force of the Sun that acts on the planet. e) None of the above statements are true.

13.7.5. The mean distance between the Earth and the Sun is 1.5 × 1011 m. Using this fact and your knowledge of the period of the Earth’s orbit around the Sun, determine the approximate mass of the Sun. a) 2 × 1014 kg b) 2 × 1018 kg c) 2 × 1024 kg d) 2 × 1027 kg e) 2 × 1030 kg

13.7.6. A satellite is in a circular orbit around the Earth. If it is at an altitude equal to twice the radius of the Earth, 2RE, how does its speed v relate to the Earth's radius RE, and the magnitude g of the acceleration due to gravity on the Earth's surface? a) b) c) d) e)

13.7.7. It is the year 2121; and people are designing a new space station that will be placed in a circular orbit around the Sun. The orbital period of the station will be 6.0 years. Determine the ratio of the station’s orbital radius about the Sun to that of the Earth’s orbital radius about the Sun. Assume that the Earth’s obit about the Sun is circular. a) 2.4 b) 3.3 c) 4.0 d) 5.2 e) 6.0

13.7.8. A space probe is orbiting a planet on a circular orbit of radius R and a speed v. The acceleration of the probe is a. Suppose rockets on the probe are fired causing the probe to move to another circular orbit of radius 0.5R and speed 2v. What is the magnitude of the probe’s acceleration in the new orbit? a) a/2 b) a c) 2a d) 4a e) 8a

13.8.1. In a galaxy far away, two stars of identical mass m = 1.0 × 1020 kg are orbiting one another at a distance of 100 million meters. What is their tangential speed in their orbit? a) 8.2 m/s b) 11.5 m/s c) 54 m/s d) 111 m/s e) 132 m/s

13.9.1. Which of the following statements best represents Albert Einstein’s reasoning that light should be deflected by gravity? a) If one were moving close to the speed of light, one would see light deflected. Therefore, gravity must also deflect light. b) Since the vacuum speed of light has a constant value for all observers, moving observers would observe light deflected by gravity. c) Newton’s law of gravity must apply to all things in the Universe; therefore, gravity must deflect light. d) As objects move closer to the speed of light, their mass increases. Light traveling at the speed of light must have mass; therefore, light is deflected by regions of higher gravity. e) An observer that is accelerated would observe a deflection of light; therefore, gravity should also deflect light.

13.9.2. Imagine that you are a future astronaut on an interstellar flight. At one point in your journey, your ship is accelerating at a rate of 7.35 m/s2. If your weight on Earth is W, what would you feel your weight is on the ship as it is accelerating? a) zero newtons, because the ship is in interstellar space b) W c) 0.75W d) 0.25W e) 0.05W

Halliday/Resnick/Walker Fundamentals of Physics 8 th edition