# Homework Help: Iv'e got every value except velocity initial and acceleration. help ?

1. Sep 11, 2010

### pokeefer

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

An accelerating lab cart passes through two photo gate timers 3.0 m apart in 4.2 s. The velocity of the cart at the second timer is 1.2 m/s (4 marks)

a.) What is the cart’s velocity at the first gate?

b.) What is the acceleration?

2. Relevant equations

v = vi + at
Vaverage = d/t
d = vi(t) + 0.5 at^2

3. The attempt at a solution

d = 3m
t = 4.2 seconds
vf = 1.2 m/s
vi = ?
a = ?

I have tried all of those formulas and they have at least 2 unknowns afterwards.

The question is worth 4 marks so velocity initial can't be 0.

2. Sep 11, 2010

### AC130Nav

posted in error.

3. Sep 11, 2010

### pokeefer

Does that mean this question is invalid?

And if so should I write this as my answer and just hand it in?

4. Sep 12, 2010

### AC130Nav

No, it means what I'd posted didn't address your problem, and having submitted I couldn't just delete the whole thing. Sorry for being ambiguous

See if you can find this formula in your book: For uniform acceleration Vavg = (Vf + Vi)/2.

From that and what you've already got, you can get Vi, which lets you get a.

Last edited: Sep 12, 2010