When will velocities of the trains equal?

  • Thread starter Thread starter Entr0py
  • Start date Start date
  • Tags Tags
    Trains
Click For Summary

Homework Help Overview

The problem involves two trains: one moving at a constant velocity and another accelerating from rest. The original poster seeks to determine the time at which their velocities become equal, given that the second train starts accelerating 20 seconds after the first train has already been in motion.

Discussion Character

  • Exploratory, Conceptual clarification, Problem interpretation

Approaches and Questions Raised

  • Participants discuss the assumptions regarding the motion of the trains, particularly the constant velocity of the first train and the acceleration of the second train. There are questions about how to calculate the distance traveled by each train and when their velocities will match.

Discussion Status

The discussion is ongoing, with participants clarifying the problem statement and attempting to establish a common understanding of the scenario. Some guidance has been offered regarding the distances traveled by the trains, but confusion remains about specific details and calculations.

Contextual Notes

There is an emphasis on the need for clarity in the problem statement, as well as the assumption that the second train accelerates at a constant rate. Participants are encouraged to specify what aspects of the problem are confusing them to facilitate better discussion.

Entr0py
Messages
102
Reaction score
1

Homework Statement


A train having a velocity of x m/s is caught by a train accelerating from zero 20 seconds after the second train starts. At what time were their velocities equal?

Homework Equations

The Attempt at a Solution


I was thinking that you'd have to assume that the train with x velocity is traveling with constant velocity and that the second train starts at t=t-20 s. However, I'm confused as to how I would find when their velocities would be equal.
 
Physics news on Phys.org
How far does the first train travel?
 
So in 20 s, the first train has traveled x=x0+v0t+.5at^2. well I assumed it started from rest, so x=.5a(400) or 200a m.
 
I'd call that the second train from my reading of the problem statement. Let's tidy up the statement a bit so we're both discussing the same trains. "Train A is moving at a constant velocity of x m/s. As it pulls even with Train B, Train B accelerates from 0 at a constant rate, and pulls even with A after 20 seconds. At what time are the two velocities equal?"

Now, I ask how far does Train A travel?
 
I'm sorry I'm confused?
 
Entr0py said:
I'm sorry I'm confused?
You need to say exactly what is confusing you. Bystander's description of the problem is correct. I'll try to make it more concrete.
At t=0, both trains are at s=0. Train A is moving at constant speed x, train B is stationary.
Train B then accelerates at some unknown constant (we must assume) rate a. At t=20, the trains have traveled the same distance. Train B must now be moving faster than train A.
At what time was train B moving at speed x?

Bystander is asking you, first, how far train A traveled in those 20 seconds.
 

Similar threads

  • · Replies 84 ·
3
Replies
84
Views
5K
Replies
3
Views
1K
Replies
20
Views
2K
  • · Replies 2 ·
Replies
2
Views
2K
  • · Replies 8 ·
Replies
8
Views
4K
  • · Replies 3 ·
Replies
3
Views
5K
  • · Replies 3 ·
Replies
3
Views
2K
  • · Replies 17 ·
Replies
17
Views
4K
  • · Replies 20 ·
Replies
20
Views
3K
  • · Replies 6 ·
Replies
6
Views
2K