physics
posted by Anonymous .
A Cessna aircraft has a liftoff speed of 120 km/h.
(a)What minimum constant acceleration does this require if the aircraft is to be airborne after a take=off of 240m?
Work: 120 km/h>33.3 m/s
(33.3 m/s)^2= (16.7 m/s)^2 + 2a(240 m)
a= 1.73 m/s^2
[What did I do wrong?]
(b)How long does it take the aircraft to be airborne?
Answer in back of book: (a) 2.32 m/s^2
(b) 14.4 s

Why do you think it had a starting velocity? Most airplanes start at the end of the runway with zero velocity.

how would I find part(b)?

I got the right answer, but the calculation does not make sense.
(240m)/(33.3 m/s) x 2 = 14.4s 
why would you multiply by 2?

Part 2.
time= distance/average velocity
or
vf= vi+ at at takeoff, solve for t.
33.3=0+2.32 t 
I got the answer to Part A and B.
Part A. (33.3)^20(velocity initial) / 2(240) = a
1108.89/480 = 2.32 (rounded)
Part B. (240m)(33.3m/s) x 2 = 14.4