Property of stress-tensor in flat spaces

Question

Let $T_{ab}$ be a stress-tensor in a flat space satisfying conservation equations. Define $$ P^i=\int T^{oi}d^3x, \;\; D^i=\int T^{00}x^id^3x $$

Can anyone show me how to prove $$ \frac{dD^i}{dt}=P^i $$

and $$ \frac{dP^i}{dt}=0 $$ ?