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

  • Thread starter Henrybar
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  • #1
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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
 
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Answers and Replies

  • #2
435
13
Just get the final velocity in m/s then convert to km/h. That would be the simplest thing to do.
 
  • #3
berkeman
Mentor
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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
Δd=1350m
= 1.35km

Vf^2=Vi^2 + 2aΔd
Vf=2.84km/h

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

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. :smile:
 
  • #4
AlephZero
Science Advisor
Homework Helper
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Vf=2.84km/h

Not sure if I did it right

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 :smile:

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?
 

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