Dr. Hwang,
 
A question concerning your projectile simulation with air drag.  I am trying to plug in parameters to simulate a car traveling through the air.  Assuming that your drag force of the form F=-kv^2 is equivalent to the drag force of the form D=.5(rho)S(Cd)*v^2, I was assuming your use of SI units and calculating your k to be equal to .5*1.25*1.1m^2*1.2; therefore, coming up with a k=.825.  Placing -0.825 into the k= box and making the velocity = 20 (assuming this to be 20m/s), I am getting no x,y coordinate pairs and a time value that is very long.  Assuming that you are using a Runge-Kutta 4th order approximation, I am very interested in the results of this simulation.  Any insight into what I am doing wrong would be much appreciated.

Thanks in advance.