Physics Review QuestionUnit:
MechanicsYear:
1993 Question#:
15Spacecraft S is traveling from planet P1 toward planet P2. At the position shown, the magnitude of the gravitational force of planet P1 on the spacecraft is equal to the magnitude of the gravitational force of plane P2 on the spacecraft. As the spacecraft moves from the position shown toward planet P _{2}, the rato of the gravitational force of P_{2} on the spacecraft
to the gravitational force of P_{1} on the spacecraft will(1
) decrease(2
) increase(3
) remain the sameWhat is this question really asking?
Explanation by: Kristina A [ Return to question menu
]Answer 1
decrease INCORRECT Before the spacecraft started moving the gravitational forces between the spacecraft and P _{1} and between the spacecraft and P_{2} were equal. The ratio of P_{2}:P_{1} is 1:1. If the ratio of P_{2}:P_{1} were to decrease, it would mean that the gravitional force between P_{2} and the spacecraft would decrease as it moved closer to P_{2}. However, as an object moves closer to a mass, the gravitational force should increase.
The contradiction proves the answer incorrect.
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Answer 2
increase CORRECT Before the spacecraft started moving the gravitational forces between the spacecraft and P _{1} and between the spacecraft and P_{2} were equal. The ratio of P_{2}:P_{1} was 1:1. As the spacecraft moves toward P_{2} the gravitational force between the spacecraft and P_{2} increases, while the gravitational force between the spacecraft andP P1 decreases.
Therefore the ratio of P_{2}:P_{1} increases.
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Answer 3
remain the same INCORRECT Before the spacecraft started moving the gravitational forces between the spacecraft and P _{1} and between the spacecraft and P_{2} were equal. The ratio of P_{2}:P_{1} was 1:1. If the ratio of P_{2}:P_{1} were to remain the same when the spacecraft were moving toward P_{2} it would mean that the gravitaional forces between the spacecraft and P_{2} would remain equal to the gravitational force between the spacecraft and P_{1}. However, as the spacecraft moves toward P_{2} the gravitational force between the spacecraft and P_{2} increases. Therefore, this choice is incorrect.return to top
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What's this question really asking?
The question is testing your knowledge of gravitational force and the effect of it on different masses. Don't let the fact that the question asks you about ratio fool you. Just use your knowledge that as moving mass moves toward another mass, the gravitaional force increase and vice versa. return to top |

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