Constant Acceleration of car over distance

1. Sep 8, 2008

Mglafas

I'm trying to do the following problem:

A car can accelerate and brake with constant acceleration, both with the magnitude (a). The car has a maximum velocity (v). The car needs to cover the distance (L), starting and ending at rest.

a) How long will it take the car to cover the distance if the maximum velocity (v) is NOT reached?

b) How long will it take the car to cover the distance if the maximum velocity (v) IS reached?

I only become increasingly confused the more I try to understand this question. If the car does not reach its maximum velocity in the first question, then how will it do so in the second when the acceleration and distance is a constant?

If I ignore (v), then i get this:
S=0.5at^2
(L/2)=0.5at^2
t=sqrt(aL)

Can anyone help?

2. Sep 8, 2008

ibc

I think what they meant in the questions is (a) solve it IF the car does not reach maximum velocity, (b) solve it IF the car does reach maximum velocity.
so you don't know what are L,a,v, so you don't know which one is true, therefore you must solve both cases, but you can't say (a) is true and (b) is not.