• Support PF! Buy your school textbooks, materials and every day products Here!

1-D motion problem

  • Thread starter hb1
  • Start date
  • #1
hb1
2
0
(a) A red train traveling at 71.8 km/h and a green train traveling at 143.6 km/h are headed toward one another along a straight, level track. When they are 950.9 m apart, each engineer sees the other's train and applies the brakes. The brakes decelerate each train at the rate of 1.017 m/s2. Is there a collision?

I got the answer: yes.

Second part of the problem (where I'm stumped):

(b) If so, what is the speed of each train at impact?

For simplicity's sake, I tried adding the distances each train would travel if it were heading in the positive x direction (positive velocity, negative acceleration) to get 950.9 m. In other words, I wrote:

V-naught-R * t + 1/2 * a * t^2 + V-naught-G * t + 1/2 * a * t^2 = 950.9

Then I tried to solve the quadratic equation for t, but I get imaginary numbers.. so there must be something wrong with my equation. HELP!!!!!

Edit: Sorry, this should probably be in the high school forum.
 
Last edited:

Answers and Replies

  • #2
StatusX
Homework Helper
2,563
1
Check your math again, but if you keep getting imaginary numbers, that would make sense only if the trains don't actually collide, so you should check your work in the first part.
 
  • #3
hb1
2
0
No, my dad figured it out. The reason I was getting imaginary numbers is because the red train is already stopped when the collision occurs. Whoever set the problem up is creative. But I'm not amused.
 

Related Threads for: 1-D motion problem

  • Last Post
Replies
2
Views
1K
  • Last Post
Replies
8
Views
621
  • Last Post
Replies
5
Views
1K
  • Last Post
Replies
1
Views
442
  • Last Post
Replies
3
Views
2K
  • Last Post
Replies
3
Views
1K
  • Last Post
Replies
11
Views
2K
  • Last Post
Replies
5
Views
4K
Top