# TEST tomorrow in physics and need help on this problem

1. Sep 11, 2008

### john16O

1. The problem statement, all variables and given/known data

A light-rail train going from one station to the next on a straight section of track accelerates from rest at 1.4 { m/s^2} for 15 { s}. It then proceeds at constant speed for 1100 { m} before slowing down at 2.2 { m/s^2} until it stops at the station.

What is the distance between the stations?

How much time does it take the train to go between the stations?

2. Relevant equations
(vx)f= (vx)i + ax$$\Delta$$t
xf= xi + (vx)i$$\Deltat$$ + 1/2ax($$\Deltat$$)2

(vx)f2= (vx)i2+2ax$$\Deltax$$
3. The attempt at a solution

I already know the answer but I cant figure out how to get to the right answer....
d= 1400m
t=77s

2. Sep 11, 2008

### jessdragon

Split the question into three different parts. Use equations Vf = Vo + at, x= 1/2(Vf + Vo)t.

For the first part, you are given Vo, a, t. You need to first find Vf, then x.

For the second part, you are given x and constant v. You must find t. Think about the units.

For the third part, you are given a (remember, it's deccelerating so it's - ), Vo, and Vf. Find t, then x.

At the end, add up all the times from the 3 parts to get 77s. And add the displacements together to get 1400m (I got 1357.5m, but 1400m is correct for the number of sig figs).

I hoped that helped, and that it wasn't too much information on how to solve the question.