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Gr. 12 Physics-Gravitational Energy Etc. I need help

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dunesquirrel
Posts: 464 - Karma: 70
Is there anyone who is knowledgeable to answer a few question for me?
May 13 2012 3:06PM
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kingcomet32
Posts: 638 - Karma: 13
post the questions
May 13 2012 3:17PM
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Black.Bird
Posts: 2566 - Karma: 684
Fire away
May 13 2012 3:17PM
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dunesquirrel
Posts: 464 - Karma: 70
awesome.

1) what is the total amount of energy needed to place a 2000 kg satellite in circular Earth orbit, at an altitude of 5.0 x 10^2 km?

2)A space shuttle ejects a 1200 kg booster tank so that the tank is momentarily at rest at an altitude of 2000 km. Neglecting atmospheric effects, determine:

a) how much work is done on the booster by the force of gravity in returning it to the Earth's surface?

b) The velocity with which it strikes the surface of the Earth?

2) A space vehicle, launched as a lunar probe, arrives at the upper limit of the Earth's atmosphere. At this point, its kinetic energy is 5.0 x 10^9 J and its gravitational potential energy is -6.4 x 10^9 J. What is its binding energy?

Any help is greatly appreciated! thanks
May 13 2012 3:31PM
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bustinthejus
Posts: 2419 - Karma: 74
2 is like grade 11 shit dude, and 1 and 3 look easy if you have the formulas, which your teacher should've given you...
May 13 2012 3:34PM
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Black.Bird
Posts: 2566 - Karma: 684
1) Use E=mgh.
E= (2 000 000 g)(9.8m/s^2)(500 000m)
= 9.8 x 10^12 N

May 13 2012 3:39PM
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theabortionator
Posts: 51263 - Karma: 157,459
1) 27 catfish

2) Ravioli

3)Afterbang
May 13 2012 3:41PM
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dunesquirrel
Posts: 464 - Karma: 70
is two the change in kinetic energy? and for 3, Binding Energy= Escape Energy- Kinetic Energy. But how do i find the escape energy from gravitational?
May 13 2012 3:42PM
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Black.Bird
Posts: 2566 - Karma: 684
Sorry I don't have time to type everything but..
2) a) = 1.8 x 10^10 J
b) = 5.5 x 10^3 m/s

It's just plugging numbers in the formulas
May 13 2012 3:43PM
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dunesquirrel
Posts: 464 - Karma: 70
Thanks. correct answers. what formulae did you use?

May 13 2012 3:45PM
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Black.Bird
Posts: 2566 - Karma: 684
For three just add the two. 5.0 x 10^9 + (- 6.4 x 10^9) = - 1.4 x 10^9
May 13 2012 3:49PM
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Bill.Nye
Posts: 4060 - Karma: 2,109
I think this should help OP

May 13 2012 3:52PM
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dunesquirrel
Posts: 464 - Karma: 70
word thanks a lot. 10/10. i got 2 a. I guess i just miscalculated but still unsure of how you found velocity for b?

May 13 2012 3:53PM
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Black.Bird
Posts: 2566 - Karma: 684
for b)

Use v = Sqrt ( 2 Ke/mass)
May 13 2012 3:56PM
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dunesquirrel
Posts: 464 - Karma: 70
what? i haven't even learned that. Is there any other way to do it?
May 13 2012 3:59PM
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Black.Bird
Posts: 2566 - Karma: 684
I don't think so?
Ke is what you calculated for a) (1.8) and I don't know what else you could use
May 13 2012 4:03PM
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dunesquirrel
Posts: 464 - Karma: 70
never mind. I realized it  is the same as GM/r. Thanks a lot man
May 13 2012 4:04PM
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Black.Bird
Posts: 2566 - Karma: 684
^No problem bud, good look with the physics. I never took grade 12 physics and took the super condensed dual physics course in first year and it sucked. Good move on your part..
May 13 2012 4:09PM
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edai
Posts: 4983 - Karma: 4,632
You're most likely in your 4th semester, does it really matter if you do your homework...
May 13 2012 4:13PM
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dunesquirrel
Posts: 464 - Karma: 70
call me what you want but i do have to maintain a decently high average going into engineering and losing good work habits is probably not a good idea


May 13 2012 4:34PM
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Darth.Maul
Posts: 2472 - Karma: 652
Ya all of these should be able to be solved with one of the GM/r equations. I just cant remember which one is which and im taking a test on it tomorrow...
May 13 2012 10:38PM
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jibjim
Posts: 1814 - Karma: 10
wrong! you've got to figure out the orbital velocity and include kinetic, not just potential
May 13 2012 11:53PM
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Black.Bird
Posts: 2566 - Karma: 684
My bad, I'm not a physics major! at least I tried..
I've also never done anything with orbital velocity.
May 14 2012 12:00AM
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Darth.Maul
Posts: 2472 - Karma: 652
Orbital velocity : (GM/r)^1/2
Escape velocity: (2GM/r)^1/2

Are those what you're looking for?
May 14 2012 12:04AM
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chicken
Posts: 6843 - Karma: 2,122
have they all been answered for you? If not let me know which one you need and I will show you
May 14 2012 12:15AM
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Parks.
Posts: 5612 - Karma: 1,093
Potential energy (gravitational) = mass x height x gravity (9.8 m/s)
May 14 2012 1:40AM
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chicken
Posts: 6843 - Karma: 2,122
not sure if this was said before, but that is not true. It is an approximation which works fine for small heights (like for instance throwing a bowling ball off of the leaning tower). however when you are using a large change in height (and therefor r) you will need to use the real definition.
May 14 2012 7:36PM
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dispatchQ_main
Posts: 2619 - Karma: 629
EASIEST CLASS, just make a crib for all the equations
May 14 2012 7:38PM
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dunesquirrel
Posts: 464 - Karma: 70
all of my questions were answered. thanks a lot everyone, definitely helped and i think i did well on my test today.
May 14 2012 8:26PM
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chicken
Posts: 6843 - Karma: 2,122
the whole thing is rearranging a couple formulas. physics doesn't get hard until it gets all full of partial derivatives and surface integrals and stuff.
May 14 2012 9:00PM
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Black.Bird
Posts: 2566 - Karma: 684
Nightmare
May 14 2012 9:48PM
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