Influenced by the gravitational pull of a distant star, the velocity of an asteroid changes from from +21.0 km/s to ?17.8 km/s over a period of 1.97 years.
(a) What is the total change in the asteroid's velocity? (Indicate the direction with the sign of your answer.)
(b) What is the asteroid's average acceleration during this interval? (Indicate the direction with the sign of your answer.)