A body of mass 2kg is projected from the ground with a velocity $20{\text{ms}}^{-1}$ at an angle $30°$ with the vertical. If ${\text{t}}_{\text{1}}$  is the time in seconds at which the body is projected and ${\text{t}}_{\text{2}}$ is the time in seconds at which it reaches the ground, the change in momentum in ${\text{kgms}}^{-1}$ during the time $\left({\text{t}}_{\text{1}}-{\text{t}}_{\text{2}}\right)$ is