Physics
posted by Geri .
a jetliner traveling northward is landing with a speed of 80 m/s. Once the jet touches down, it has 800 m of runway in which to reduce its speed to 10 m/s. (a) Compute the average acceleration (magnitude and direction) of the plane during landing (take the direction of the plane's motion as positive). (b) How long a runway does the jetliner need to stop?

WEll, it is headed north, with a negative acceleration.
it takes d=800 to slow down.
Vf^2=Vi^2+2ad
a= (1006400)/2*800=54/15 m/s^2 S
what is d if Vf=0?
0^2=6400+2(54/15)d