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Hint 3

The pericentre distance is

\begin{displaymath}r_1=a(1-\epsilon)=200\; {\rm km}\end{displaymath}

which corresponds to 190 km above the surface.

The period (which is equal to that for a circular orbit of radius $a$) is

\begin{displaymath}T=2\pi\sqrt{a^3\over GM}=16\; {\rm days}\end{displaymath}

since the mass of the asteroid is $M=1.1\times 10^{16}$ kg.

The energy (also equal to that for a circular orbit of radius $a$) is

\begin{displaymath}E=-{GMm\over 2a}\end{displaymath}

Hence the energy must decrease by

\begin{displaymath}\Delta E={GMm\over 2a}=570\; {\rm J}\end{displaymath}

since the energy of a parabolic orbit is zero.

The maximum speed occurs at pericentre where the energy can be written

\begin{displaymath}E={1\over 2}mv_1^2-{GMm\over r_1}\end{displaymath}

Using the total energy above gives

\begin{displaymath}v_1=\sqrt{GM\left({2\over r_1}-{1\over a}\right)}=2.3\;{\rm ms}^{-1}\end{displaymath}



Mike Birse
2001-03-22