51) Why did Newton think there was force acting on the moon? 52) Suppose the gravitational force between two massive spheres is 20 N. If the distance between the spheres is doubled, what is the force between the masses? 53) Suppose the gravitational force between two massive spheres is 20 N. If the magnitude of each mass doubles, what is the force between the masses? 54) Since Earth is attracted to the sun, why doesn’t it fall into the sun? 55) A 600-N woman stands on top of a very tall ladder so she is one Earth radius above Earth’s surface. How much does she weigh?

 56) Suppose the gravitational force between two masses is 20 N. If the volume of each mass doubles, while everything else stays the same, what is the force between the masses? 57) Why is it that it is so difficult to detect gravitational forces between ordinary objects? 58) A very massive object A and a less massive object B move toward each other under the influence of mutual gravitation. Which is greater, the force on A, or the force on B? 59) According to Newton’s laws, a rock and a pebble will fall at the same acceleration in a gravitational field. Explain this in terms of the mass and weight of the objects. 60) Each of us weighs a tiny bit less on the ground floor of a skyscraper than we do on the top floor. One reason for this is that ___________

 61) What did Newton hypothesize about the moon? 62) Two objects move toward each other because of gravitational attraction. As the objects get closer and closer, what happens to the force between them? 63) Why doesn’t the moon fall into the Earth? 64) If the mass of Earth increased, with no change in radius, what would happen to your weight? 65) Newton reasoned what relationship between gravitational attraction and the distance between objects like the Earth and the moon?

 66) Jupiter has more than 300 times the mass of Earth. Yet on Jupiter’s surface an object weighs only about 3 times as much as it would on Earth. Why is this? 67) A hollow spherical planet is inhabited by people who live inside it, where the gravitational field is zero. When a very massive space ship lands on the planet’s surface, how does the gravitational field change within the planet? Why? 68) A lunar month is about 28 days. If the moon were closer to Earth than it is now, what would happen to the lunar month? 69) A supplier wants to make a profit by buying metal by weight at one altitude and selling it at the same price per pound at another altitude. Where should the supplier buy and where should he sell? Would altitude have a significant effect? 70) If Earth’s mass decreased to one half its original mass, with no change in radius, what would happen to your weight?

 71) Suppose the gravitational force between two massive spheres is 20 N. If the distance between the spheres is cut in half, what is the force between the masses? 72) Newton had the insight about the forces on the moon and an apple. What was it? 73) By noticing that Uranus’s orbit is perturbed and by using the law of gravitation, two astronomers independently discovered ____________ 74) If you stood atop a ladder on Earth that was as tall as Earths radius (so you were twice as far from Earth’s center) what would happen to your weight atop the ladder? 75) Consider the gravitational force between the earth and a meteor in outer space. If the meteor moves so its distance from the earth’s center doubles, what happens to the gravitational force on the meteor? The gravitational force on the earth?

 76) If the radius of Earth decreased, with no change in mass, what would happen to your weight? 77) Is the force of gravity on you greatest when you are standing on the earth’s surface, slightly above the earth’s surface, or slightly below the earth’s surface? Why? 78) If you burrow deeply into a planet what will happen to the force of gravity on you? What will happen if the planet’s radius simply shrinks with you remaining on the surface? 79) Compare the gravitational force between Earth and Mars, and the gravitational force between a newborn baby and the doctor who holds it. The greater force is between ___________ 80) Which is greater, the gravitational force between Earth and the moon, or between Earth and the sun?

 TRUE/FALSE. If true, mark “A”, if false; mark “B” on the Scantron T/F 81) What are the two possible outcomes of the expansion of the universe? T - F 82) Because Earth and moon are gravitationally attracted towards each other, will they soon collide? Explain. T - F 83) Does the force on a ball decreases as the ball moves farther from Earth? Explain in terms of Newton’s gravitational equation. T - F 84) If Earth were to disappear, would the moon still orbit the place where Earth was? Explain why or why not. T - F 85) What is the name of the component of an orbiting satellite’s velocity that is parallel to Earth’s surface? T - F 86) The force of attraction between two masses depends inversely on the square of the distance between the masses. What is the name for any law that has this kind of dependence on distance? T - F 87) If Earth were its present size but twice as massive, what would happen to our weight? T - F 88) Is there is a force on Earth that is directed toward the sun? T - F 89) Because Earth is “falling” around the sun, will it eventually fall into the sun? Why or why not? T - F