Formula Help (1 Viewer)

[GlowYossy22]

Hey everyone,

I need help deciding on which formula to use for a specific question. The marking guideline records: calculates centripetal force via correct formula, calculation and answer.

I need to find the force acting on a satellite, in this situation the satellite is 450 kg and is orbiting 35,9000 km above the earth. It is one part of a multipart question, the next questions ask what the velocity is and what is the orbital period. Would I be correct using centripetal force = mv^2 / r, by using the velocity I calculated in the second part of the question or do I have to use F = GMm / r^2

 

[ExtremelyBoredUser]

Hey everyone,

I need help deciding on which formula to use for a specific question. The marking guideline records: calculates centripetal force via correct formula, calculation and answer.

I need to find the force acting on a satellite, in this situation the satellite is 450 kg and is orbiting 35,9000 km above the earth. It is one part of a multipart question, the next questions ask what the velocity is and what is the orbital period. Would I be correct using centripetal force = mv^2 / r, by using the velocity I calculated in the second part of the question or do I have to use F = GMm / r^2
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I'm sure both ways are valid but;

If you found the velocity in the next question, you can't simply assume that value of velocity in your Q without doing the working out, I doubt you can say v = (some value) as shown from [insert next question] [at least its not permitted for me]. If you just do the working out for calculating velocity again, find it then use that value for centripetal force, then it should be valid as long as it aligns with the other formula.

Personally that's too much effort for using the centripetal force formula and the question is designed in such a way that the Gravitational Law formula is more apparent since it gives radius + mass of satellite and you can simply find mass of the earth on the reference sheet. Then you just plug in the values and you get the same answer. I believe this is the way the markers expect you to solve the question - so my guess is that this the "correct" formula.

 

[XXXPUMPERXXX]

The formula for the orbital velocity is derived from the combination of centripetal force and gravitational force anyways so should be fine either way.

 

[GlowYossy22]

I asked my teacher, she didn't reply with an answer but instead this:

i - Any physics problem that involved circular motion or orbital motion is likely to incude the orbital radius (r) as a factor in the calculation.
ii - in general the group of formulae we refer to in this unit is directly related to Newton's second law so the following should help...

I guess she wants me to use f = mv/r^2