Homework Help: 1-D motion problem

(a) A red train traveling at 71.8 km/h and a green train traveling at 143.6 km/h are headed toward one another along a straight, level track. When they are 950.9 m apart, each engineer sees the other's train and applies the brakes. The brakes decelerate each train at the rate of 1.017 m/s2. Is there a collision?

I got the answer: yes.

Second part of the problem (where I'm stumped):

(b) If so, what is the speed of each train at impact?

For simplicity's sake, I tried adding the distances each train would travel if it were heading in the positive x direction (positive velocity, negative acceleration) to get 950.9 m. In other words, I wrote:

V-naught-R * t + 1/2 * a * t^2 + V-naught-G * t + 1/2 * a * t^2 = 950.9

Then I tried to solve the quadratic equation for t, but I get imaginary numbers.. so there must be something wrong with my equation. HELP!!!!!

Edit: Sorry, this should probably be in the high school forum.

 

No, my dad figured it out. The reason I was getting imaginary numbers is because the red train is already stopped when the collision occurs. Whoever set the problem up is creative. But I'm not amused.