MCAT Physics Question — Satellite Orbit
 by
 Oct 23, 2014
 MCAT Question of the Day
A satellite of mass m_{s} is orbiting a planet at a speed v_{s}. The planet has a mass M_{p}. Which of the following represents the radius of the satellite’s orbit measured from the center of the planet?
A) GM_{p} / v_{s}^{2}
B) √(GM_{p}m_{s} / v_{s})
C) ½ (m_{s}v_{s}^{2})
D) Gm_{s} / v_{s}^{2}
Explanation
An object travelling in circular orbit is experiencing a centripetal force from the planet’s gravity. We may thus set up the following equation:
Fc = GM_{p}m_{s} / r^{2} = m_{s}v^{2} / r
Cancelling the mass of the satellite we get:
GM_{p} / r^{2} = v^{2} / r
Multiply both sides by the radius of the orbit:
GM_{p} / r = v^{2}
The question asked for the radius of the orbit, so isolate r:
GM_{p} / v^{2} = r
Thus, choice (A) is the right answer.
If you’re not sure how to proceed, always try to eliminate one or two choices before you guess. If you couldn’t remember the equations for centripetal force or for gravity, you may still have been able to recognize choice (C) as the kinetic energy equation. The question asked you for radius, so an answer choice that would be in joules would have to be wrong. So eliminate (C) and guess.
Want more MCAT practice?
We’ve got options for every schedule and learning style!
From the best online MCAT course created by top instructors with 524+ MCAT scores to the most representative fulllength practice exams and private tutoring, we can custom tailor your MCAT prep to your goals!
Not sure which option is right for you? Schedule a free MCAT consultation with an MCAT expert using the form below. No obligation, just expert advice.
Search the Blog
Free Consultation
Interested in our Online MCAT Course, OneonOne MCAT Tutoring or Med admissions packages? Set up a free consultation with one of our experienced Senior Student Advisors.
Schedule NowPopular Posts

MCAT Blog How to Review MCAT FullLengths
Free MCAT Practice Account
Need great MCAT practice?Get the most representative MCAT practice possible when you sign up for our free MCAT Account, which includes a halflength diagnostic exam and one of our fulllength MCAT practice exams.
Learn More
Submit a Comment