#ifndef RELATIVISTIC_ROCKETH
#define RELATIVISTIC_ROCKETH
#include <cmath>       //for sqrt
#include "rocket.h"
using namespace std;

class relativistic_rocket: public rocket {
public:
	relativistic_rocket(double initial_length, double initial_v);

	//speed of light in vacuum (meters per second)
	static double c() {return 2.99792458e8;}

	double length() const {
		return rocket::length() * sqrt(1 - v() * v() / (c() * c()));
	}
};
#endif