# Amtrak's 20th-Century Limited is in route from Chicago to New York at 112 km/h, when,

## Homework Statement

Amtrak's 20th-Century Limited is in route from Chicago to New York at 112 km/h, when the engineer spots a cow on the track. The train brakes to a halt in 2.3 min, stopping in front of the cow.

a) What is the magnitude of the train's (constant) acceleration?
_______m/s^2 <-----(0.22m/s^2) Correct

b) What is the direction of the acceleration?
- eastward
- westward <-----Correct
- southward
- northward

c) How far was the train from the cow when the engineer first applied the brakes?
______km

## The Attempt at a Solution

I have a) and b) correct but I can't figure out c).

Thanks.

## Answers and Replies

reverse it. imagine the train is accelerating at 0.22 m/s/s

LowlyPion
Homework Helper

## Homework Statement

Amtrak's 20th-Century Limited is in route from Chicago to New York at 112 km/h, when the engineer spots a cow on the track. The train brakes to a halt in 2.3 min, stopping in front of the cow.

a) What is the magnitude of the train's (constant) acceleration?
_______m/s^2 <-----(0.22m/s^2) Correct

b) What is the direction of the acceleration?
- eastward
- westward <-----Correct
- southward
- northward

c) How far was the train from the cow when the engineer first applied the brakes?
______km

## The Attempt at a Solution

I have a) and b) correct but I can't figure out c).

Thanks.

First what equation do you know that relates distance acceleration and time?

(Btw, I think the 20th Century Limited stopped running in 1967. Today it's the Lake Shore Limited that runs the route.)

First what equation do you know that relates distance acceleration and time?

(Btw, I think the 20th Century Limited stopped running in 1967. Today it's the Lake Shore Limited that runs the route.)

I know this equation but I get the wrong answer: d=(vf^2-vi^2)/2a

LowlyPion
Homework Helper

I know this equation but I get the wrong answer: d=(vf^2-vi^2)/2a

I would have simply used the x = 1/2 a t2 relationship.

x = 1/2 * .22544 * (138 sec)2

The other equation works as well

x = (31.111)2/(2*(.22544))