TEST tomorrow in physics and need help on this problem

  • Thread starter john16O
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  • #1
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Homework Statement



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?

Homework Equations


(vx)f= (vx)i + ax[tex]\Delta[/tex]t
xf= xi + (vx)i[tex]\Deltat[/tex] + 1/2ax([tex]\Deltat[/tex])2

(vx)f2= (vx)i2+2ax[tex]\Deltax[/tex]

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
 

Answers and Replies

  • #2
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.
 

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