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In the following pairs of length units, which is the shortest: Inch and centimeter? Yard and meter? Mile and kilometer? |
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2 | |
What is the minimum number of unequal forces whose vector sum can equal zero? |
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3 | |
Is it correct to say that scalar quantities are abstract, idealized quantities with no precise counterparts in the physical world, whereas vector quantities properly represent reality because they take directions into account? |
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4 | |
Can anything have an acceleration in the opposite direction to its velocity? If so, give some examples. |
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5 | |
What happens to the speed of an object as it falls freely? To its acceleration? |
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6 | |
Can anything ever have a downward acceleration greater than g? If so, how can this be accomplished? |
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7 | |
Suppose you are in a barrel going over Niagara Falls and during the fall you drop an apple inside the barrel. Would the apple appear to move toward the top of the barrel or toward the bottom, or would it remain stationary within the barrel? |
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8 | |
(a) Imagine that Charlotte drops a ball from a window on the twentieth floor of a building while at the same time Fred drops another ball from a window on the ninteenth floor of that building. As the balls fall, what happens to the distance between them (assuming no air resistance)? (b) Next imagine that Charlotte and Fred are at the same window on the twentieth floor and that Fred drops his ball a few seconds after Charlotte drops hers. As the balls fall, what happens to the distance between them now (again assuming no air resistance)? |
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9 | |
A person in a stationary elevator drops a coin and the coin reaches the floor of the elevator 0.6 s later. Would the coin reach the floor in less time, the same time, or more time if it were dropped when the elevator was (a) falling at a constant speed? (b) falling at a constant acceleration? (c) rising at a constant speed? (d) rising at a constant acceleration? |
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10 | |
A movie seems to show a ball falling down. From what appears on the screen, could you tell whether the movie is actually showing a ball being thrown upward but the film is being run backward in the projector? |
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11 | |
Every acceleration is the result of a force. Does every applied force produce an acceleration? |
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12 | |
Consider the statement: Sara weighs 55 kg. What is wrong with the statement? Give two ways to correct it. |
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13 | |
Distinguish between mass and weight. |
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14 | |
Albert is standing still on the ground. Does this mean that there is no gravitational force acting on him? If such a force is acting on him, why is he not moving? |
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15 | |
Since the opposite forces of the third law of motion are equal in magnitude, how can anything ever be accelerated? |
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16 | |
When you whirl a ball at the end of a string, the ball seems to be pulling outward away from your hand. When you let the string go, however, the ball moves along a straight path perpendicular to the direction of the string at the moment you let go. Explain each of these effects. |
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17 | |
A book rests on a table. (a) What is the reaction force to the force the book exerts on the table? (b) To the force gravity exerts on the book? |
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18 | |
Two children wish to break a string. Are they more likely to succeed if each takes one end of the string and they pull against each other, or if they tie one end of the string to a tree and both pull on the free end? Why? |
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19 | |
An engineer designs a propeller-driven spacecraft. Because there is no air in space, the engineer includes a supply of oxygen as well as a supply of fuel for the motor. What do you think of the idea? |
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20 | |
Show from its defining formula that the unit of centripetal force is the newton. |
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21 | |
Under what circumstances, if any, can something move in a circular path without a centripetal force acting on it? |
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22 | |
A car makes a turn on a level road at too high a speed and its left wheels leave the road. Was the car turning to the left or to the right? |
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23 | |
A track team on the moon could set new records for the high jump or pole vault (if they did not need space suits, of course) because of the smaller gravitational force. Could sprinters also improve their times for the 100-m dash? |
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24 | |
If the moon were twice as far from the earth as it is today, how would the gravitational force it exerts on the earth compare with the force it exerts today? |
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25 | |
Compare the weight and mass of an object at the earth's surface with what they would be at an altitude of two earth's radii. |
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26 | |
A hole is bored to the center of the earth and a stone is dropped into it. How do the mass and weight of the stone at the earth's center compare with their values at the earth's surface? |
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27 | |
Is the sun's gravitational pull on the earth the same at all seasons of the year? Explain. |
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28 | |
According to the theory of gravitation, the earth must be continually "falling" toward the sun. If this is true, why does the average distance between earth and sun not grow smaller? |
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29 | |
According to Kepler's second law, the earth travels fastest when it is closest to the sun. Is this consistent with the law of gravitation? Explain. |
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30 | |
A "geostationary" satellite does not appear to move across the sky but remains over the same place on the earth's equator. Why doesn't it fall to the ground? |
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31 | |
An artificial satellite is placed in orbit half as far from the earth as the moon is. Would the satellite's time of revolution around the earth be longer or shorter than the moon's if its orbit is to be stable? |
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32 | |
Is an astronaut in an orbiting spacecraft actually "weightless"? |
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33 | |
An airplane makes a vertical circle in which it is upside down at the top of the loop. Will the passengers fall out of their seats if there is no belt to hold them in place? |
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