# Gravity Question

Discussion in 'MCAT Study Question Q&A' started by TheRealAngeleno, Aug 18, 2011.

1. ### TheRealAngeleno

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Hey guys I have a quick question on this problem. So I narrowed it down to C & D since since a centrifugal force is not really a force and I ended up picking D. I can't seem to understand the answer explanation but wouldn't there be a centripetal force due to the result of gravity and therefore the answer would be D. The answer is C btw. Thanks.

What type of force(s) act on an orbiting satellite in space?

I. A Centrifugal Force
II. A Centripetal Force
III. A Gravitation Force.

A. I only
B. I and II only
C. III only
D. II and III only

2. ### tn4596 5+ Year Member

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it should have centripetal force, i think D is correct.

3. ### EyEnStein 07 Senior ɸ Member 10+ Year Member

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Hm I can see why this question is a little confusing. Usually in orbit cases, the centripetal force is provided by the gravitational force. Perhaps that's why the answer is Gravitational only? (i believe this is true for all orbits).

On another note, im quite surprised to see Centrifugal force on there. It might have just been my UG but when i took calc based physics i definitely did not hear of Centrifugal. It was only in Classical Mechanics that I learned that it is a fictitious force opposing the centripetal force.

4. ### neurodoc Neurologist 10+ Year Member

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You are correct that the only "real" force acting on the satellite is the gravitational attraction between the earth and the satellite, and that this is a centripetal force, so D is the correct answer, and if the "approved" answer is C, that is a mistake. In this example, there is no centrifugal force. However, there are some situations where there is a "real" centrifugal force and not just a "fictitious" force that's useful for making calculations. This involves a real "reactive" centrifugal force that's based on Newton's principle of "equal and opposite" reaction. It doesn't apply in the inertial frame used to analyze satellite orbits.

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