# Converting m/s^2 to km/h^2 ?

1. Feb 18, 2014

### Henrybar

An airplane starts from rest and accelerates at a constant rate of 3.00 m/s^2 for 30.0s before leaving the ground. What is the airplanes velocity in km/h at the end of this interval?

Vi=0m/s
Vf=?
a=3m/s^2
Δt=30s

Not sure if I did it right or if im also supposed to convert the acceleration to km/h before plugging into equation. If so, how do i convert 3m/s^2 to km/h^2?? Please help

Last edited: Feb 18, 2014
2. Feb 18, 2014

### Panphobia

Just get the final velocity in m/s then convert to km/h. That would be the simplest thing to do.

3. Feb 18, 2014

### Staff: Mentor

You are given acceleration and time, not acceleration and distance. You need to use a different version of the kinematic equation -- one that relates velocity to acceleration and time...

And to do any units conversion, just multiply by "one". So if I wanted to convert inches to mm, for example, I'd multiply by 1 = (25.4mm/1 inch), cancel the "inch" units on the top and bottom of the fraction, and be left with the distance in mm.

4. Feb 18, 2014

### AlephZero

Check your answer using common sense. At that speed, if you were late for the check-in, you would be able to walk down the runway (not even run) and catch up the plane to get on the flight

Also, it's not "wrong" to find the distance and then the speed (if you do it right), but why not use the formula Vf = Vi + at?