# Homework Help: Need help finding Kinematic formula for Initial V

1. Sep 10, 2009

### Krasz

1. The problem statement, all variables and given/known data
A truck covers 60.0 m in 9.0s while smoothly slowing down to final speed 3.00 m/s.
Find the initial velocity.

2. Relevant equations
Vi +1/2at^2 has two unknowns
V= vo + at has two unknowns
x= v^2 - Vi^2/2a has two unknowns
v^2=vi^2 +2a(xf-xi) has two unknowns

3. The attempt at a solution
I have been scouring the internet looking for a formula that can solve for V initial excluding acceleration that can work! I can't seem to find any! How do I go about finding the initial velocity?

2. Sep 10, 2009

### Fightfish

Variables you have: final velocity v, displacement s, and time t. Which one of the four classic kinematics equations excludes the acceleration a?

3. Sep 10, 2009

### Krasz

I can't believe I overlooked that! Thank you!

4. Sep 10, 2009

### rl.bhat

You have to use two equations
vf = vi - at.......(1)
x = vi*t - 1/2*a*t^2 ......(2)
substitute the value of vi from the first equation in the second equation and solve for vi.