// http://en.wikipedia.org/wiki/Escape_velocity

#include <stdio.h>
#include <stdlib.h>
#include <math.h>

//Earth
//    Mass:    5.9736e24
//    Readius: 6400 kilometers
//    Escape velocity: 11.2 km/s
//
//Sun
//    Mass:    1.989e30
//    Readius: 695500 km
//    Escape velocity: 617.7 km/s

double m2km(double d)
{
    return d*1000.0;
}

double ms2kms(double speed)
{
    return speed/1000.0;
}

double calcEscapeVelocity(double M, double G, double r)
{
    return sqrt(2*G*M/r);
}

int main(int argc, char* argv[])
{
    double M,G,r;

    // G = 6.67*pow(10,-11);  // universal gravitational constant
    G = 6.67e-11;  // universal gravitational constant

    double a = 2e3;
    printf("%f\n", a);

    printf("Enter the planet's mass (in kg): ");
    scanf("%lf", &M);

    printf("Enter the planet's radius (in km): ");
    scanf("%lf", &r);

    r = m2km(r);

    double speed = calcEscapeVelocity(M,G,r);
    speed = ms2kms(speed);

    printf("The escape velocity is %.1f km/s\n", speed);

	system("pause");
	return 0;
}