# A passenger train is traveling at 27 m/s when the engineer s

1. Sep 13, 2015

### argpirate

1. The problem statement, all variables and given/known data
A passenger train is traveling at 27 m/s when the engineer sees a freight train 366 m ahead of his train traveling in the same direction on the same track. The freight train is moving at a speed of 5.9 m/s.
(a) If the reaction time of the engineer is 0.39 s, what is the minimum (constant) rate at which the passenger train must lose speed if a collision is to be avoided?

2. Relevant equations
dx=vt+1/2at^2

3. The attempt at a solution
I tried to set the dx=dx and solve for t using the quadratic equation. Then, since we are solving for minimum maginitude of decceleration I set the discriminant (containing 'a') equal to zero so I would get the smallest acceleration magnitude and a real time. But it was marked wrong.

2. Sep 13, 2015

### SteamKing

Staff Emeritus
It would be better if you posted your actual calculations, rather than describe verbally the procedure you followed.

3. Sep 13, 2015

### argpirate

but i did it wrong. If you do it the same way, you will know you did it wrong like me when you read it

4. Sep 13, 2015

### SteamKing

Staff Emeritus
But that's the thing. You want someone to tell you what you did wrong. How is anyone able to do this without checking your actual work? You may have used the wrong procedure, you may have made an arithmetic mistake, etc.

This is Physics Forums, not Psychics Forums. There's no shame in posting erroneous calculations here; people do it all the time.

5. Sep 13, 2015

### argpirate

i am sure i did it wrong. I just want to know how to do it right.