program escape
      
C************************************************************
C   Compute the required escape velocity needed given different
C	radii of the earth and moon in addition to the distance
C	between the earth and the moon.
C
C   Known values:  radius of earth = 4000 km
C		   radius of moon = 1000 km
C	           E-M distance = 240000 km
C*************************************************************

      parameter(g=9.8)
      real velYesMoon, velNoMoon, r_earth, r_moon, distanceEM
      
      print *, 'Enter radius of Earth (km): '
      read *, r_earth
      
      print *, 'Enter radius of Moon (km): '
      read *, r_moon
      
      print *, 'Enter Earth-Moon distance (km): '
      read *, distanceEM
      
C-----CONVERT MEASUREMENTS INTO METERS
      r_earth = r_earth * 1000.0
      r_moon = r_moon * 1000.0
      distanceEM = distanceEM * 1000.0
      
      velYesMoon = sqrt((2.0*g*r_earth) -
     + ((200.0 * r_earth**2.0)/(81*(distanceEM+r_moon+r_earth))) +
     + ((2.0*g*r_earth**2.0)/(81*(distanceEM+r_moon))))
     
      print *, 'Escape velocity accounting for moon: ',velYesMoon

      velNoMoon = sqrt(2.0 * g * r_earth)

      print *, 'Escape velocity with no moon: ', velNoMoon

      print *, 'Difference in velocities: ', velNoMoon-velYesMoon

      stop
      end