A child runs down his driveway with an initial speed of 3.0 m/s for 4.5 s, and then uniformly decreases his speed to 0.0 m/s in 2.5 s. What is the boy’s acceleration during the second part of his motion?
he starts at 3.0m/s, ends at zero m/s, in 2.5 seconds
a=changevelocty/time