(a) By definition of average acceleration,
a = ∆v / ∆t = (0 - 38 m/s) / (5.0 s)
a = -7.6 m/s²
(b) Recall that
v² - u² = 2 a ∆x
where u and v are initial and final velocities, respectively; a is acceleration; and ∆x is the change in position. So
0² - (38 m/s)² = 2 (-7.6 m/s²) ∆x
∆x = 95 m
