# Airplane down the runway

1. Aug 31, 2006

### WRXSIG

airplane down the runway....

An airplane travels 277m down the runway before taking off.
Assuming that it has constant acceleration, if it starts from rest and becomes airborne in 8.00 seconds, how fast m/s is it moving at takeoff?

am i missing something here? 277/8seconds =34.6m/s?

2. Aug 31, 2006

### jdog

yes, I'm afraid you are. What you have calculated is it's average velocity, the total displacement divided by the total time. To find the velocity at take off, you first have to find what that constant acceleration is, then see how fast it's going after 8 seconds of accelerating at that rate.

you need these two equations:

x(t) = 1/2 a t^2 (assuming it starts from rest at the origin)

and

v(t) = a*t (assuming it starts from rest)

3. Aug 31, 2006

### rcgldr

It's easier than that, with constant acceleration, average velocity is 1/2 the final velocity.

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