v=dr/dt=d(2ti+(2-t？ )j)/dt=2i-2tj

Substitute t= 1s and t=2s into the above formula to get: v 1=2i-2j and v2=2i-4j.

2. Take the first derivative of the above velocity equation to get the acceleration:

A=dv/dt=d(2i-2tj)/dt=-2j. Obviously, the acceleration is a constant value, so a 1=a2=-2j.