# Homework Help: Find the height of a free falling object

1. Feb 15, 2015

### KwamKwam

1. The problem statement, all variables and given/known data
An object falls freely, moving 60m in the last 2 seconds. Find the height at which it was dropped.

2. Relevant equations
Vf = 1/2(gt^2) + Vo(t)+ Yo
g= 9.8m/s^2

3. The attempt at a solution
the object accelerates at 9.8m/s^2 . and the velocity would be 30m/s. (60 divided 2) so do you plug in 30m/s and the acceleration of gravity and solve for Yo? (the initial position)

2. Feb 15, 2015

### BvU

Dag KwamKwam, welcome to PF

You want to check your equation -- or precisely describe what you mean with Vf. Otherwise the dimensions don't fit.
To me it looks as if two equations from here have been squashed together. And you need both, I think.

3. Feb 15, 2015

### KwamKwam

Thank you, Vf is the objects final velocity

4. Feb 15, 2015

### BvU

You still want to check your equation. On the left you have m/s, on the right you have m + m/s + m . Can't be right !
Can you make sense of the expressions in the link I gave ?

5. Feb 15, 2015

### KwamKwam

yeah I can. so my equations are V = Vo+ a(t) and X=Xo + Vo(t) + 1/2(at^2) instead of my first one?

6. Feb 15, 2015

### BvU

Very good. a(t) and V0(t) are confusing. Better write a t and V0 t or a $\times$ t and V0 $\times$ t

Now you have these two equations you want to sort out how to apply them. What to fill in, how to choose t = 0 and x = 0 and such. Any ideas ?

7. Feb 15, 2015

### KwamKwam

so X0 = 60, t = 2 and a = -9.8 and V0is what we're searching for.

8. Feb 15, 2015

And X=?