I need help with these physics questions! (2 Viewers)

[SanjanaSenthil]

1. A satellite with mass 200kg maintains a stable orbit of 300km above the Earths surface. Determine the Gravitational Potential Energy of the satellite.

2. A 2000kg satellite is to be placed in a circular orbit 8000km above the Earths surface. The radius of the Earth is 6380km.

a) Calculate the GPE of the satellite before launch.
b) Calculate the GPE of the satellite in orbit,
c) Calculate the work done against gravity to raise the satellite to this height.
d) Explain why the energy needed to place a satellite in orbit is greater that the work required to lift the satellite to the correct height.

3. Two asteroids in deep space each have a mass of M kg and are separated by r km. The gravitational potential energy of the asteroid is E joules.
If separation between the asteroids were to decrease to r/2 km, describe the resulting gravitational potential energy.

Thanks!!!

 

[kunal96]

1. Ep=-Gm1m2/d
(6.67x10^-11*200*5.97*10^24)/(6.37*10^6+300000)
=1.194*10^10

 

[SanjanaSenthil]

I got -1.194 x 10^10..how did you get a positive answer?

 

[kunal96]

2.
a) -1.25*10^11
b) -5.54*10^10

 

[nerdasdasd]

I got -1.194 x 10^10..how did you get a positive answer?

He probably just got lazy.

 

[WeaselPowa]

I got -1.194 x 10^10..how did you get a positive answer?

You can't get a positive answer for GPE, hence why the formula has a negative sign. But the textbook should also explain why it's a negative :O

 

[SanjanaSenthil]

Ohh I see, just read the text book. Thank you Yay, I got the answers right so far except for 1 which is meant to be positive.

 

[kunal96]

yah i got lazy :/

 

[kunal96]

wait is the answer to part c) 6.96*10^10?
(btw i havent done the space topic at school yet)

 

[sprytex]

wait is the answer to part c) 6.96*10^10?
(btw i havent done the space topic at school yet)

How'd you get that?

I got 1.57*10^11 J.

 

[kunal96]

wait how do you calculate part c)?

 

[sprytex]

wait how do you calculate part c)?

I just used Work = Fs = mgh

not sure if it's the right thing to use though...

 

[WeaselPowa]

According to memory, I think mgh only applies within Earth. For things such as the satellite which orbit outside of the Earth's surface, the other formula's apply. (Look in the Excel textbook if you have it)

 

[kunal96]

yeah im pretty sure the answer to part c) is -6.96*10^10

 

[SanjanaSenthil]

If by any chance there is a teacher reading this who stars with W, hello

 

[sprytex]

According to memory, I think mgh only applies within Earth. For things such as the satellite which orbit outside of the Earth's surface, the other formula's apply. (Look in the Excel textbook if you have it)

Yeah I thought so, since g changes with height.

yeah im pretty sure the answer to part c) is -6.96*10^10

Which equation did you use?

 

[SanjanaSenthil]

I got -5.68 x 10^10 for C..

 

[SanjanaSenthil]

Nope scratch that, I got 1.57 x 10^11

 

[kunal96]

i reckon the answer is 6.96*10^10. (and im sure it's without the negative sign this time) Also if you dont mind me asking, which textbook/where are you getting these questions from?

 

[someth1ng]

1. Ep=-Gm1m2/d
(6.67x10^-11*200*5.97*10^24)/(6.37*10^6+300000)
=1.194*10^10

If that was a 3 mark question, you would get 1/3.

Incorrectly using the formula (neglecting - sign).
Incorrect answer because it is positive.

For Work Done, it is Ep(final)-Ep(initial), if you're lifting against gravity, it is positive (c). Don't forget, 'd' is distance in metres from the other CENTRE OF MASS in METRES.