Unit: Mechanics
Year: 1993 Question#: 15
Spacecraft 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 P2, the rato of the gravitational force of P2 on the spacecraft to the gravitational force of P1 on the spacecraft will
(1 ) decrease
(2 ) increase
(3 ) remain the same
What is this question really asking?
Explanation by: Kristina A
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Answer 1
decrease
INCORRECT
Before the spacecraft started moving the gravitational forces between the spacecraft and P1 and between the spacecraft and P2 were equal. The ratio of P2:P1 is 1:1. If the ratio of P2:P1 were to decrease, it would mean that the gravitional force between P2 and the spacecraft would decrease as it moved closer to P2. However, as an object moves closer to a mass, the gravitational force should increase. The contradiction proves the answer incorrect. return to top
Answer 2
increase
CORRECT
Before the spacecraft started moving the gravitational forces between the spacecraft and P1 and between the spacecraft and P2 were equal. The ratio of P2:P1 was 1:1. As the spacecraft moves toward P2 the gravitational force between the spacecraft and P2 increases, while the gravitational force between the spacecraft andP P1 decreases. Therefore the ratio of P2:P1 increases. return to top
Answer 3
remain the same
INCORRECT
Before the spacecraft started moving the gravitational forces between the spacecraft and P1 and between the spacecraft and P2 were equal. The ratio of P2:P1 was 1:1. If the ratio of P2:P1 were to remain the same when the spacecraft were moving toward P2 it would mean that the gravitaional forces between the spacecraft and P2 would remain equal to the gravitational force between the spacecraft and P1. However, as the spacecraft moves toward P2 the gravitational force between the spacecraft and P2 increases. Therefore, this choice is incorrect.
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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
