\magnification = \magstep2

$$
\eqalign{
E \ \ = \qquad   KE_{i} \ \ + \ \ GPE_{i} \ \   &=  \ \ KE_{f} \ \ + \ \  GPE_{f} \cr
\cr
  {{1}\over{2}} m v_{i}^2 + {-{G M_{E} m}\over{R_{E}}} 
         &=  {{1}\over{2}} m v_{f}^2 + {-{G M_{E} m}\over{R_{f}}} \cr 
\cr
  {{1}\over{2}} m v_{i}^2 - {{G M_{E} m}\over{R_{E}}} 
         &=  {{1}\over{2}} m 0^2 - {{G M_{E} m}\over{\infty}} \cr 
\cr
  {{1}\over{2}} m v_{i}^2 - {{G M_{E} m}\over{R_{E}}} 
         &=  0  -  0 \cr
\cr
  {{1}\over{2}} m v_{i}^2 - {{G M_{E} m}\over{R_{E}}} 
         &=  0 \cr
}
$$

$$
  {{1}\over{2}} m v_{esc}^2 = {{G M_{E} m}\over{R_{E}}}  
$$

$$
  v_{esc} = \sqrt{{{2 G M_{E} }\over{R_{E}}}}  
$$


\bye
\end
