Projectile Motion 2D -- Spring Launched There is this ball launched from a slingshot. Given the mass is 0.9 kg at the angle 60° to the horizontal, with k=750 N/m and is stretched by length l = 0.6 m. The ball is shot 1 m above the ground. (g=10 m/s2). The questions are to derive the equation describing the velocity and trajectory with the aerodynamic drag negligible. My approach is first to find the acceleration in x and y direction. F = k.x = 750x0.6 = 450 N Fx = F cos 60 = 389.71 N, Fy = F sin 60 = 225 N Horizontal: Fx = m*ax ax = 250 m/s2 Vertical: Fy - mg = m*ay ay = 423.01 m/s2 Then I find the Velocity Vx = Vox + 250t Vy = Voy + (423.01-10)t = Voy + 413.01t My problem is now finding the initial Velocity Vo. I was thinking of using Energy principal but then I am stuck with the velocity of the ball at certain point, thus, I was not able to solve it.