How long will it take the bus to come to a complete stop? I do not know how to write this out or iam missing something. the answer is 2 sec. but I can not get that. please help me see where I am off. thank you

You need to find when the speed is zero, this would mean the bus comes to a complete stop. Since the speed after braking is given by:

f=80-20t

^{2},setting this equal to zero yields:

80-20t

^{2}=0 Or 80=20t^{2}, which leads tot

^{2}=80/20=4, from which it is easy to see that**t=2 seconds**