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Thread: gravity and energy problems

  1. #1
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    gravity and energy problems

    A 920kg satellite is projected vertically upward from Earth's surface with an initital kinetic energy of 7.0x10^9J. Find
    a)its max height
    b)the initital kinetic energy it would have needed to keep going indefinitely
    c)the inital speed it would have needed to keep going indefinitely.

    which equations would I use for each part?
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  2. #2
    Senior Member topher0805's Avatar
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    I'm not very good at helping people with math, but I'll give it a shot.

    Perhaps you can use the physics formula, $\displaystyle v=\sqrt{\frac{2K}m}$ to figure out initial velocity.

    The acceleration due to gravity is $\displaystyle 9.8m/s^2$. However, you can not simply use $\displaystyle d=vt + \frac{1}2at^2$ to figure out the max height because as you get farther from earth, gravity decreases.

    What you need to do is use the gravitational constant, G. It is approximately equal to $\displaystyle 6.67 x 10^-11$.

    Hmm, this is harder than I thought. I'll have to think about it for a while.
    Last edited by topher0805; Feb 6th 2008 at 09:13 PM.
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  3. #3
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    I wasn't able to get the correct answers from using the above formulas. Are there different equations I can use?
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