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Math Help - calculus- plz help..

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    calculus- plz help..

    The weight (force due to gravity) of an object of mass m and altitude x miles above the surface of the earth is w(x) = (mgR^2)/(R+x)^2, where R is the radius of the earth and g is the acceleration due to gravity. Show that w(x) is approximately mg(1-2x/R). Estimate how large x would need to reduce the weight by 10%.
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    Quote Originally Posted by bobby77
    The weight (force due to gravity) of an object of mass m and altitude x miles above the surface of the earth is w(x) = (mgR^2)/(R+x)^2, where R is the radius of the earth and g is the acceleration due to gravity. Show that w(x) is approximately mg(1-2x/R). Estimate how large x would need to reduce the weight by 10%.
    I solved your first question in another post.

    To get an estimate on x, we are looking for an x such that the weight is .9w(0)=.9mg.

    w(x) = .9mg \approx mg \left ( 1- \frac{2x}{R} \right )

    Now solve for x. (This assumes x is small enough to use the above approximation. You should always check that this is true once you get your answer for x.)

    -Dan
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