ex2.f90

program energy
  != unit kg :: mass
  != unit m/s**2 :: gravity
  != unit m :: height
  real, parameter :: mass = 3.00, gravity = .81, height = 4.20

  != unit kg m**2/s**2 :: potential_energy
  real :: potential_energy
 
  potential_energy = mass * gravity * height
end program energy