\left\{x''(t)=-\frac{c y(t) x'(t) f\left(\sqrt{x'(t)^2+y'(t)^2}\right)}{\sqrt{x'(t)^2+y'(t)^2}},y''(t)=-\frac{c y(t) y'(t) f\left(\sqrt{x'(t)^2+y'(t)^2}\right)}{\sqrt{x'(t)^2+y'(t)^2}}-g\right\}