A plank fitted with a gun is moving on a horizontal surface with speed of `4m//s` along the positive x-axis. The z-axis is in vertically upward direction. The mass of the plank including the mass of the gun is 50 kg. When the plank reaches the origin, a shell of mass 10 kg is fired at an angle of `60^@` with the positive x-axis with a speed of `v = 20m//s` with respect to the gun in x-z plane. Find the position vector of the shell at t=2 s after firing it. Take `g = 9.8 m//s^2`.