A cracker is thrown into air with a velocity of `10 m//s` at an angle of `45^(@)` with the vertical. When it is at a height of `0.5 m` from the ground, it explodes into a number of pieces which follow different parabolic paths. What is the velocity of centre of mass, when it is at a height of `1 m` from the ground? (`g = 10 m//s^(2)`)