'''
Name:Brian Lam
Date: Oct 06 2011
Description: This program will calculate the escape velocity, given the input of
circumference of the planet, and acceleration due to gravity.
'''

#Declares Global Constants
PI = 3.14159265
GRAVITY_CONSTANT = 6.67428*10**-11

#Defines the main function
def main():
    circumference = input ('Circumference (m) of  planet? ')
    acceleration = input ('Acceleration due to gravity (m/s^2)? ')
    escape_velocity(circumference, acceleration)

#Defines the function, escape_velocity with parameters
def escape_velocity(circumference, acceleration):
    radius = ((circumference /PI) / 2)
    mass = ((acceleration * (radius**2)) / GRAVITY_CONSTANT)
    vescape = (((2 * (GRAVITY_CONSTANT * mass)) / radius))**0.5
    display_results (radius, mass, vescape)

#Defines the function, display_results
def display_results (radius, mass, vescape):
    print ' '
    print 'Calculating the escape velocity...'
    print 'Planet radius = % .1f km' % (radius/1000)
    print 'Planet mass = %.1f x 10^21 kg' % (mass/10**21)
    print 'Escape Velocity = % .1f km/s' % (vescape/1000)

main()