Airplane Braking Distance Question

[physicsgurl12]

Homework Statement

Assuming equal rates of acceleration in both cases how much further would you travel if braking from 56mi/h to rest than from 28mi/h ?
a, 5.2 times farther
b, 4.8 times farther
c, 3.2 times farther
d, 4.0 times farther

Homework Equations

not really sure what i should use.
v=v0+at
x= x0+2a(x-x0)

The Attempt at a Solution

0-56/0-28=56/28=2

 

[Valedictorian]

V1 (56 m/s) is twice as great as V2 (28 m/s) so the time needed to stop is going to be doubled, due to a the equal acceleration. So you take the difference in the velocity values (twice as great), and in the time values (twice as great), and you come up with the four times farther by multiplying the aforementioned values.

 

[physicsgurl12]

ohh. thank you!