# Finding Time If you know Accel, Vi and distance

1. Sep 12, 2011

### student54321

1. The problem statement, all variables and given/known data
Some aircraft are capable of accelerations
of magnitude 42.5 m/s2. If an aircraft starts
from rest, how long will it take the aircraft
to travel down the 2.6-km runway?

2. Relevant equations
d= vi(t) - 1/2 a(t)2

I am assuming that you need to solve for t. I had trouble altering the equation to do that.

3. The attempt at a solution
since velocity initial is 0m/s, I keep getting divide by zero error, and I get a cube root.

Last edited: Sep 12, 2011
2. Sep 12, 2011

### cepheid

Staff Emeritus
Welcome to PF student54321,

Divide by zero error???

If vi = 0, then vit = 0, and the equation becomes:

d= 0 + (1/2)at2

Note that the second term should have a + sign, not a - sign, although typically 'a' also has an intrinsic sign depending on whether the acceleration is positive or negative.

This becomes:

d= (1/2)at2

Now can you solve for t?

Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook