Distance to stoppage

1. Jul 10, 2010

Canha

1. The problem statement, all variables and given/known data

Train goes at 280km/h. Starts breaking with a constant acceleration of -2m/s-2. How many meters does it perform until it stops completely? Sorry if the English is poor.

2. Relevant equations

3. The attempt at a solution

Well, 280km/h equals to about 77.78 m/s. Great, what now?

2. Jul 10, 2010

Karmalo

If you are gonna do kinematic exercises you should know the basic equations.

$$v=v_{0}+at$$
$$v^{2}=v^{2}_{0}+2ae$$
$$x=x_{0}+v_{0}t+\frac{1}{2}at^{2}$$

Try with those, one should work, and write them down for the next problems.

3. Jul 10, 2010

mizzy

ok. that's a start. =) write down your knowns: v initial, v final, a. Your unknown is distance.

4. Jul 10, 2010

Canha

I do know the first and third, but those don't seem to help do they? What do I do with the time in there? I don't have any reference to the time. What's the 'e' in the second one?

EDIT: Oh, should I discover the time at which the final v is at 0 and then substitute in the motion equation to find out the position?

Last edited: Jul 10, 2010
5. Jul 10, 2010

mizzy

look at your knowns and look at the equations.

e is distance

6. Jul 10, 2010

mizzy

Don't need to find time!

7. Jul 10, 2010

Canha

But would it work?
Anyway I never heard about the second equation but it did work! I don't understand but it did lol.

8. Jul 10, 2010

mizzy

those are the 3 main equations to know for constant acceleration

9. Jul 10, 2010

Canha

I don't think I would pull this off in an exam (now I would).

Thank you both!

10. Jul 10, 2010

mizzy

you're welcome =)