Answer: a = 0.4 m/s^2
t = 50 s
Explanation:
Convert 72 km/hr to m/s by multiplying it by (1000 m / 1 km)(1 hr / 3600s).
Then, plug this into the formula: (v final)^2 = (v original)^2 + 2*a*d; v original = 0, so it becomes 20^2 = 2*a*500. This yields a = .4 m/s^2.
For the time: a = change in speed / t, which becomes .4 = 20 / t, which yields t = 50 s.
