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# A satellite in a circular orbit rotates around the Earth eve

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GRE Instructor
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A satellite in a circular orbit rotates around the Earth eve [#permalink]  05 Aug 2019, 09:40
Expert's post
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Question Stats:

60% (01:53) correct 40% (00:00) wrong based on 5 sessions
A satellite in a circular orbit rotates around the Earth every 120 minutes. If the Earth’s radius is 4000 miles at sea level, and the satellite’s orbit is 400 miles above sea level, approximately what distance does the satellite travel in 40 minutes?

A. 1400 miles
B. 9210 miles
C. 4400 miles
D. 4120 miles
E. 8000 miles
[Reveal] Spoiler: OA

_________________

Brent Hanneson – Creator of greenlighttestprep.com

Intern
Joined: 31 Jul 2019
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Re: A satellite in a circular orbit rotates around the Earth eve [#permalink]  06 Aug 2019, 05:05
No explanation?
The at sea level and above sea level kind of muddles my understanding, can someone clarify that?
GRE Instructor
Joined: 10 Apr 2015
Posts: 2290
Followers: 71

Kudos [?]: 2165 [0], given: 26

Re: A satellite in a circular orbit rotates around the Earth eve [#permalink]  06 Aug 2019, 05:43
Expert's post
GreenlightTestPrep wrote:
A satellite in a circular orbit rotates around the Earth every 120 minutes. If the Earth’s radius is 4000 miles at sea level, and the satellite’s orbit is 400 miles above sea level, approximately what distance does the satellite travel in 40 minutes?

A. 1400 miles
B. 9210 miles
C. 4400 miles
D. 4120 miles
E. 8000 miles

This diagram might help

So, the black dot represents the Earth's center.
So, the radius of the satellite's orbit = 4400 miles

circumference of circle = 2πr

So, the circumference of satellite's orbit = 2π(4400) = 8800π

GIVEN: the satellite in a circular orbit rotates around the Earth every 120 minutes.
In other words, the satellite travels 8800π every 120 minutes

So, in 40 minutes, the satellite will travel 1/3 of the 8800π mile orbit (since 40 minutes is 1/3 of 120 minute)

Distance traveled = 8800π/3

PRO TIP: Since π ≈ 3.14, we know that π/3 ≈ 3.14/3 ≈ some number a little bit bigger than 1

So, 8800π/3 = 8800(π/3) = 8800(a number a little bit bigger than 1) = some number a little bit bigger than 8800

Cheers,
Brent
_________________

Brent Hanneson – Creator of greenlighttestprep.com

Re: A satellite in a circular orbit rotates around the Earth eve   [#permalink] 06 Aug 2019, 05:43
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