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March 29, 2017

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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

  • Physics - ,

    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)

  • Physics - ,

    how do i get small r?

  • Physics - ,

    is it R_e + height?

  • Physics - ,

    Yes, earth radius + height

  • Physics - ,

    (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.

  • Physics - ,

    both terms should be positive

  • Physics - ,

    What do you mean?

  • Physics - ,

    (6.67E-11*220*5.98E24)/[2(6.38E6+2.0E5)]
    note 2 in denominator
    + (6.67E-11*220*5.98E24) / 2^10^5

  • Physics - ,

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

  • Physics - ,

    so is it 6770873457?

  • whoops error - ,

    Change in Potential energy to lift it to orbit
    = G m M [1/Rearth - 1/r ]

  • Physics - ,

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

  • Physics - ,

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

  • Physics - ,

    7.07*10^9 Joules

  • Physics - ,

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

  • Physics - ,

    Your professor must like arithmetic !

  • Physics - ,

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

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