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Two satellites A and B of the same mass are going around Earth in concentric orbits. The distance of satellite B from Earth’s center is twice that of satellite A. What is the ratio of the centripetal force acting on B to that acting on A? 1. 1/8 2. 1/4 3. 1/2 4. √1⁄2 5. 1 Answer: 2.The centripetal force on each satellite is provided by the gravitational force between the satellite and Earth.

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Two satellites A and B of the same mass are going around Earth in concentric orbits. The distance of satellite B from Earth’s center is twice that of satellite A. What is the ratio of the tangential speed of B to that of A? 1. 1⁄2 2. √1⁄2 3. 1 4. √2 5. 2 Answer: 2. For each satellite, the centripetal force is equal to the gravitational force between the satellite and Earth, and is proportional to the square of the tangential velocity and the inverse of the distance.

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**1. be much less than g (because the ball doesn’t fall to the ground). **

Suppose Earth had no atmosphere and a ball were fired from the top of Mt. Everest in a direction tangent to the ground. If the initial speed were high enough to cause the ball to travel in a circular trajectory around 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 speed. Answer: 2.The ball’s acceleration is caused by the only force exerted on the ball: gravitation. Near the surface of Earth, the value of this acceleration is g (perhaps a little less because of the altitude of Mt. Everest).

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**The Moon does not fall to Earth because **

1. It is in Earth’s gravitational field. 2. The net force on it is zero. 3. It is beyond the main pull of Earth’s gravity. 4. It is being pulled by the Sun and planets as well as by Earth. 5. all of the above 6. none of the above Answer: 6.The Moon is accelerating toward Earth because of the gravitational attraction between the two.This attraction supplies the centripetal force necessary to keep the Moon in orbit.

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Thermodynamics

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CH 17: Temperature

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What is temperature? Temperature describes the relative hotness or coldness between two objects. If you use your hand to compare the temperature of two objects you can only tell that one is warmer than the other. Temperature is a means of comparing the “hotness” between two objects. We define a standard “hotness” and compare all objects with this standard. What is the most commonly used standard for comparing the temperatures of different objects? The typical choice for a reference is the freezing point of water. All relative temperatures are compared to this standard. The numerical value for this standard is arbitrary. When two objects are placed in contact and internal energy can be transferred from one object to the other we say these two objects are in Thermal Contact. When two objects at different temperatures are placed in contact with each other they transfer internal energy from the object with more internal energy to the object with less internal energy. This will continue until both objects reach the same temperature. Two objects that are at the same temperature are said to be in Thermal Equilibrium. This fundamental idea is the basis for the zeroth law of thermodynamics. 0th Law of Thermodynamics – If object A and object B are separately in thermal equilibrium with a third object C, then A and B are in thermal equilibrium with each other. This law essential describes how a thermometer works.

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Temperature Scales There are two temperature scales based on the 0th law of thermodynamics. These two scales are called relative scales. They are both arbitrarily based on the properties of water. Celsius Define two points 0oC and 100oC, which correspond to two distinct point where a phase change (temperature remains constant) occurs for water. All temperatures are measured relative to these specified values. Fahrenheit Define two points 32oF and 212oF, which correspond to two distinct point where a phase change (temperature remains constant) occurs for water. All temperatures are measured relative to these specified values. Both of these scales operate under the same principle, but they use a different mathematical relation to define the smallest change in the scale. These are relative scales, therefore zero has no meaning for the scale, it is just a reference point. Zero Celsius (32oF) is just the temperature at which water freezes. We can convert between the Fahrenheit and Celsius scales in the following way: There is approximately a 2o change in Fahrenheit for every 1o change in Celsius.

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