A flatcar is moving horizontally along a straight track with a constant speed $v$. A launcher mounted on the flatcar contains a small projectile of mass $m$, which is initially at rest relative to the flatcar. The launcher fires the projectile at an angle $\theta$ above the forward horizontal direction, as measured in the flatcar's reference frame. In the flatcar's frame, the projectile leaves the launcher with kinetic energy $K_0$. What is the change in the kinetic energy of the projectile, as measured in the ground frame, during the launch?