Finding how long it takes given changing acceleration

[lim]

Homework Statement

At highway speeds, a particular automobile is capable of an acceleration of about 1.57 m/s2. At this rate, how long does it take to accelerate from 72.0 km/hr to 100.0 km/hr?

Homework Equations

I was given: vf = vi + at

The Attempt at a Solution

Simplifying the velocities I got 28 = 1.57a
and a= 17.83 s.

 

[learningphysics]

Homework Statement

At highway speeds, a particular automobile is capable of an acceleration of about 1.57 m/s2. At this rate, how long does it take to accelerate from 72.0 km/hr to 100.0 km/hr?

Homework Equations

I was given: vf = vi + at

The Attempt at a Solution

Simplifying the velocities I got 28 = 1.57a
and a= 17.83 s.

careful about units... convert km/hr to m/s or convert m/s^2 to km/hr^2...