# Vertical Motion Question

1. Sep 6, 2008

### veronicak5678

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

A ball is thrown vertically from the edge of a cliff. It rises 10 m above the cliff, then falls 50 m below the cliff.
Find the inital velocity and determine the time the ball was in the air.
2. Relevant equations

(v final )^2 - (v initial)^2 = 2a (delta y)

3. The attempt at a solution

I'm not sure if I should use 10 or 60 m for the displacement in this equation.

I used 60 m and got v inital = 34. 292 m/s.

2. Sep 6, 2008

### Hootenanny

Staff Emeritus
Displacement is a vector with a magnitude equal to the distance between the initial point & final point. In this case your initial point is 0m and your final point is -50m.

3. Sep 6, 2008

### tiny-tim

Hi veronicak5678!

I don't get it … what did you use for vfinal?

(and why 60 rather than 40?)

Hint: you need at least one known v … so what y must you use?

4. Sep 6, 2008

### veronicak5678

I used 0 for v final. And I used 60 because it travels 10 above, then 50 below. So I should just use 50 for delta y?

5. Sep 6, 2008

### tiny-tim

Good … but if you use 0 for vfinal, you must use the y where v = 0, which is … ?

6. Sep 6, 2008

### veronicak5678

So I do use 50 for displacement? Using that, I come up with initial velocity = 31.3 m/s, and time in the air = 3.194 s.