A satellite of mass 220 kg is launched from a site on Earth's equator into an orbit at 200 km above the surface of Earth.

(a) Assuming a circular orbit, what is the orbital period of this satellite?
5310 s

(b) What is the satellite's speed in its orbit?
7790m/s

(c) What is the minimum energy necessary to place the satellite in orbit, assuming no air friction?

I was able to get a and b, but i don't know about c.

Thanks

User Icon for Damon Damon answered
14 years ago

You have to lift the body to orbit and then speed it up to orbit speed.

m v^2/r = G m M/r^2 in orbit
so (1/2)m v^2 = G m M/(2r) = Ke in orbit
Change in Potential energy to lift it to orbit
= G m M/(r-Rearth)

User Icon for Ana Ana answered
14 years ago

how do i get small r?

User Icon for Ana Ana answered
14 years ago

is it R_e + height?

User Icon for Damon Damon answered
14 years ago

Yes, earth radius + height

User Icon for Ana Ana answered
14 years ago

(6.67E-11*220*5.98E24)/(6.38E6+2.0E5)-(6.38E6)=

1.33295653E10J

Is this right? I want to make sure if this is right before I insert into the site.

User Icon for Damon Damon answered
14 years ago

both terms should be positive

User Icon for Ana Ana answered
14 years ago

What do you mean?

User Icon for Damon Damon answered
14 years ago

(6.67E-11*220*5.98E24)/[2(6.38E6+2.0E5)]

note 2 in denominator
+ (6.67E-11*220*5.98E24) / 2^10^5

User Icon for Damon Damon answered
14 years ago

8.78*10^16 [ 1/1.32E7 + 1/2E5 ]

User Icon for Ana Ana answered
14 years ago

so is it 6770873457?

User Icon for Damon Damon answered
14 years ago

Change in Potential energy to lift it to orbit

= G m M [1/Rearth - 1/r ]

User Icon for Damon Damon answered
14 years ago

8.78*10^16 [ 1/1.32E7 + 1/6.38E6 - 1/6.58E6 ]

User Icon for Ana Ana answered
14 years ago

this is my last try....is it 6904053501?

User Icon for Damon Damon answered
14 years ago

7.07*10^9 Joules

User Icon for Damon Damon answered
14 years ago

We are close to each other. My arithmetic is failing, after bedtime.

User Icon for Damon Damon answered
14 years ago

Your professor must like arithmetic !

User Icon for Ana Ana answered
14 years ago

Yes, we are. Some of the problems are very difficult but thank you so much for your help. I really appreciate.