# Yet Another Free Fall Problem

1. Feb 6, 2004

### holly

I have read through the other free fall problems here on the boards and still cannot correctly solve the following:
One-half second after starting from rest, a freely falling object will have a speed of about: a)10 m/s b)2.5 m/s c)5 m/s d)20 m/s

I find the answer to be (b), 2.5 m/s, but my husband assures me I am not solving it correctly...that I am not using the right formula. I am using a=dt**2 even tho I know acceleration isn't speed...but I don't know what formula to use! This is a physics for health majors class, we don't use calculus. We barely use algebra, and we're all flunking, flunking...

Can some Big Brain please provide me with the formula to solve for speed? The only time I can solve free fall probs is when we are solving for distance and then I use d=1/2gt**2.

2. Feb 6, 2004

### jamesrc

You know that the object, whatever it is, has a constant downward acceleration given by g. All you are asked for in this question is the velocity after a given time. The equation you want to use here is

$$v = v_0 + at$$

3. Feb 7, 2004

### HallsofIvy

Staff Emeritus
Acceleration is defined as "change in speed divided by change in time" of (assumingstarting from rest at t=0) a= v/t so
v= at. That's much simpler that jumping from acceleration to distance and then working back! An object falling freely under gravity, on the surface of the earth, has an acceleration of 9.8 m/s2 downward. After a half second, its speed would be
9.8m/s2(1/2 s)= 4.9 m/s. Much closer to the given 5 m/s than 2.5 m/s.-