# Coeffecient of train and the tracks?

## Homework Statement

What is the coefficient of friction between the train and the track, given that the train has 20,000 kg and is going at velocity of 26m/s. Note that when the train conductor saw a pedestrian he started braking and also the distance between the pedestrian to the train is 500m
Other given information:
X= 500m
A= -.676 ( because he was stopping the train)
braking force is -13520 N

## Homework Equations

μkN=Fk

N means normal force in this case[/B]

## The Attempt at a Solution

So at first I tried using the simple friction formula and tried isolating the coefficient of friction so that i would have ----------- μ=Nf---------- but i have everything except friction force. So i then thought from that I thought i can just divide a and m to get the force, which in turn is the friction force. Overall i am not sure if this is correct because i thought you can just divide the breaking force and the mass for the friction force. It's either one or the other, although i am not completely sure ))

In this problem, it's more about the Work done to the train to get it to come to a halt. First they give you the train's mass and velocity.
(Remember: Kinetic Energy http://www.sciweavers.org/upload/Tex2Img_1418868535/render.png [Broken] )

If we look at the the energy of the system, it goes to zero. As you've said before, there is a frictional force which acts on the system. This (frictional) Work must then equal the Kinetic Energy lost when braking the train.

Also, Work is equal to the force applied over a distance http://www.sciweavers.org/upload/Tex2Img_1418868266/render.png [Broken] .

I hope this helps point you in the right direction :)

Last edited by a moderator:
Thegiver431
haruspex
Homework Helper
Gold Member
2020 Award
i have everything except friction force
The braking force you (correctly) calculated is the friction force.

Thegiver431
Thank you for everybody that answered, I get it now :)

Narwhalest