A busy chipmunk runs back and forth along a straight line of acorns that has been set out between its burrow and a nearby tree. At some instant, it moves with a velocity of -1.39 m/s. Then, 2.29 s later, it moves with a velocity of 1.55 m/s. What is the chipmunk's average acceleration ay during the 2.29 s time interval? aav= m/s